in Drupal 7

Go to admin/structure/types/manage/article/fields and add a new field named "Tags" with the type "Term reference" and the widget "  Autocomplete term widget (tagging)"
in the setting field page, configure it to reference the vocabulary named "Tags" (if the vocabulary doesn't exist, just add it in admin/structure/taxonomy/add)


How can I create a custom module that can be reinstalled without throwing an error?

You can make your config dependent on the module by adding this to the relevant config file(s):

dependencies:
  enforced:
    module:
      - module_name

When your module is uninstalled, the config will go with it. You probably want to delete any content and field instances in hook_uninstall as well.


Drupal 7 Bartik plus theme drop down menu

The answer I found was here Changing Bartik theme to dropdown

and I used this CSS file with fixed issue

CSS file to put into superfish folder


I (and my team) wrote most of that module and -- as Jeremy says, it's only needed for extreme scalability. Because of that, it's supposed you know what you are doing (otherwise you will have no chance of scaling to the levels where MongoDB is necessary) and so no UI is provided, just use $conf overrides.

There's a DBTNG driver too but it's more in a proof-of-concept stage so it's in a separate project.