Issue title: Comments have fallen off subscriptions
 Issue body: Salespeople used to be able to add comments to subscription records, but can't now.
 Comments: 
 Comment 0: Hello I am new to Open source can I work on this?  
 Comment 1: Hey @hd719 , you are welcome to pick this up if you'd like; this is an issue related to the admin Subscriptions page, visible at `/admin/subscriptions` after running

```
User.find_by(username: "<username>").update(admin: true)
```
on your logged in user.

ActiveAdmin has some functionality for adding comments to models... for example going to `/admin/groups/:id` you can see

![image](https://cloud.githubusercontent.com/assets/750477/25156736/6d26ff00-24d7-11e7-987a-f9d989288a16.png)


So this fix would be making the same thing work for subscriptions.

Have to say this isn't very high on our list of priorities, but happy to accept a contribution if you're willing to do it.
 Comment 2: 
~~Hey @gdpelican~~

~~I am setting up the development enviroment and when I run `rake bootstrap` I keep getting this error~~



~~Hamels-MacBook-Air:loomio HD$ rake bootstrap
Hold on, project is starting
npm WARN timothywalker@example.com requires a peer of timothywalker@example.com but none was installed.
npm WARN timothywalker@example.com requires a peer of grunt@>=0.4.0 but none was installed.
Database.yml file already exists
could not connect to server: No such file or directory
        Is the server running locally and accepting
        connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `initialize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `new'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `connect'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/postgresql_adapter.rb:242:in `initialize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `new'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `postgresql_connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:438:in `new_connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:448:in `checkout_new_connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:422:in `acquire_connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:349:in `block in checkout'
/Users/HD/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:348:in `checkout'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:263:in `block in connection'
/Users/HD/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:262:in `connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_adapters/abstract/connection_pool.rb:571:in `retrieve_connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_handling.rb:113:in `retrieve_connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/connection_handling.rb:87:in `connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/postgresql_database_tasks.rb:6:in `connection'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/postgresql_database_tasks.rb:15:in `create'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/database_tasks.rb:93:in `create'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/database_tasks.rb:107:in `block in create_current'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/database_tasks.rb:275:in `block in each_current_configuration'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/database_tasks.rb:274:in `each'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/database_tasks.rb:274:in `each_current_configuration'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/tasks/database_tasks.rb:106:in `create_current'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/activerecord-116.69.203.115/lib/active_record/railties/databases.rake:17:in `block (2 levels) in <top (required)>'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:248:in `block in execute'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:243:in `each'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:243:in `execute'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
/Users/HD/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:180:in `invoke_with_call_chain'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:209:in `block in invoke_prerequisites'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:207:in `each'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:207:in `invoke_prerequisites'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:186:in `block in invoke_with_call_chain'
/Users/HD/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:180:in `invoke_with_call_chain'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:209:in `block in invoke_prerequisites'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:207:in `each'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:207:in `invoke_prerequisites'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:186:in `block in invoke_with_call_chain'
/Users/HD/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:180:in `invoke_with_call_chain'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:173:in `invoke'
/Users/HD/Projects/Open-Source/loomio/lib/tasks/bootstrap.rake:71:in `block in <top (required)>'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:248:in `block in execute'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:243:in `each'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:243:in `execute'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
/Users/HD/.rvm/rubies/ruby-2.3.1/lib/ruby/2.3.0/monitor.rb:214:in `mon_synchronize'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:180:in `invoke_with_call_chain'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/task.rb:173:in `invoke'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:152:in `invoke_task'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:108:in `block (2 levels) in top_level'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:108:in `each'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:108:in `block in top_level'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:117:in `run_with_threads'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:102:in `top_level'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:80:in `block in run'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:178:in `standard_exception_handling'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/lib/rake/application.rb:77:in `run'
/Users/HD/.rvm/gems/ruby-2.3.1/gems/rake-11.3.0/exe/rake:27:in `<top (required)>'
/Users/HD/.rvm/gems/ruby-2.3.1/bin/rake:23:in `load`
/Users/HD/.rvm/gems/ruby-2.3.1/bin/rake:23:in `<main>'
/Users/HD/.rvm/gems/ruby-2.3.1/bin/ruby_executable_hooks:15:in `eval'
/Users/HD/.rvm/gems/ruby-2.3.1/bin/ruby_executable_hooks:15:in `<main>`
Couldn't create database for {"adapter"=>"postgresql", "database"=>"loomio_development"}
could not connect to server: No such file or directory~~

** Update ** 

-Fixed this, I forgot to have postgres running. 

 Comment 3: @gdpelican 

Hey so I am trying to make my user an admin and whenever I do `User.find_by(username: "default").update(admin: true)` I get `Unknown Attribute "admin" for User` 

```
=> #<User id: 1, email: "timothywalker@example.com", created_at: "2017-04-24 19:52:04", updated_at
: "2017-04-24 19:59:06", name: nil, deactivated_at: nil, avatar_kind: "initials", uploaded_a
vatar_file_name: nil, uploaded_avatar_content_type: nil, uploaded_avatar_file_size: nil, upl
oaded_avatar_updated_at: nil, is_admin: false, avatar_initials: "DE", username: "default", e
mail_when_proposal_closing_soon: false, authentication_token: nil, unsubscribe_token: "xZ-2M
4JjZHzAzodyzZc2", memberships_count: 0, uses_markdown: false, selected_locale: nil, time_zon
e: "America/New_York", key: "GLDZsaEu", detected_locale: "en", email_missed_yesterday: true,
 email_api_key: "e2e18bc423e3072ec493092da7a8d360", email_when_mentioned: true, angular_ui_e
nabled: true, email_on_participation: false, default_membership_volume: 2, experiences: {},
country: nil, region: nil, city: nil>
2.3.1 :010 > User.find_by(username: "default").update(admin: true)
  User Load (1.5ms)  SELECT  "users".* FROM "users" WHERE "users"."username" = $1 LIMIT 1  [
["username", "default"]]
   (0.2ms)  BEGIN
   (0.2ms)  ROLLBACK
ActiveRecor38d1:d2b4:3d06:83e8:96a5:8c2:893d:aba5UnknownAttributeError: unknown attribute 'admin' for User.
```

-Thank you. 
 Comment 4: Hello any update on this? 

I even tried `User.find_by(username: "default").make_admin!` did not work I got on error saying "undefined method 'make_admin!' for #<User:0x007fce863013d8>

I got the `make_admin!` method from the 

`app/models/membership.rb` 

```
def make_admin!
  update_attribute(:admin, true)
end
```

-Thank you. 
 Comment 5: Oh... ack, sorry. The field on user is called `is_admin`, rather than `admin`.

You can check out the current column names in the database in `db/schema.rb`
 Comment 6: Hey @gdpelican so I was able to make my user an admin, but `localhost:3000/admin/subscriptions` does not work, I get an error saying "No route matches [GET] "/admin/subscriptions" .

-Thank you. 
 Comment 7: hey @gdpelican Any update on this? 
 Comment 8: Sorry @hd719 but I'm not able to provide this level of support. I'd encourage you to hack around on the project some and become more familiar with the way routing and rails works.
 Comment 9: hey @gdpelican I understand, but there is no route defined as `admin/subscriptions` and also I do not see a admins subscriptions option on the admin page. 

![screen shot 2017-05-09 at 7 35 32 pm](https://cloud.githubusercontent.com/assets/20329318/25876998/b34b7f20-34ee-11e7-9328-56f65dc32a08.png)

![screen shot 2017-05-09 at 7 35 19 pm](https://cloud.githubusercontent.com/assets/20329318/25876999/b34c1e26-34ee-11e7-949c-cd78353769ae.png)


I was wondering do you want me to create one and then add comments section to that page? 

-Thank you.  
 Comment 10: Hello @gdpelican  any update on this?


 Comment 11: Hello @gdpelican sorry for the bother any update on this?
 Comment 12: Hey @hd719 did you see GDP's earlier comment? "Sorry @hd719 but I'm not able to provide this level of support."

{'source': 'GithubIssues', 'repo_name_with_owner': 'loomio/loomio', 'issue_id': 194814889, 'repo_stars': 2134.0}