Add a basic activity as seed data
user
```ruby
# setup a simple, one-page activity
act = Lightweight::LightweightActivity.create!(:name => "Test activity")
page = act.pages.create!(:name => "Page 1", :text => "This is the main activity text.")
interactive = Lightweight::MWInteractive.create!(:name => "MW model", :url => "http://lab.dev.concord.org/examples/interactives/embeddable.html#interactives/oil-and-water-shake.json")
Lightweight::InteractiveItem.create!(:interactive_page => page, :interactive => interactive)

# Add questions
or1 = Embeddable::OpenResponse.create!(:name => "Open Response 1", :prompt => "Why do you think this model is cool?")
or2 = Embeddable::OpenResponse.create!(:name => "Open Response 2", :prompt => "What would you add to it?")

mc1 = Embeddable::MultipleChoice.create!(:name => "Multiple choice 1", :prompt => "What color is chlorophyll?")
Embeddable::MultipleChoiceChoice.create(:choice => 'Red', :multiple_choice => mc1)
Embeddable::MultipleChoiceChoice.create(:choice => 'Green', :multiple_choice => mc1)
Embeddable::MultipleChoiceChoice.create(:choice => 'Blue', :multiple_choice => mc1)

mc2 = Embeddable::MultipleChoice.create!(:name => "Multiple choice 2", :prompt => "How many protons does Helium have?")
Embeddable::MultipleChoiceChoice.create(:choice => '1', :multiple_choice => mc2)
Embeddable::MultipleChoiceChoice.create(:choice => '2', :multiple_choice => mc2)
Embeddable::MultipleChoiceChoice.create(:choice => '4', :multiple_choice => mc2)
Embeddable::MultipleChoiceChoice.create(:choice => '7', :multiple_choice => mc2)

Lightweight::QuestionItem.create!(:interactive_page => page, :question => mc1)
Lightweight::QuestionItem.create!(:interactive_page => page, :question => or1)
Lightweight::QuestionItem.create!(:interactive_page => page, :question => or2)
Lightweight::QuestionItem.create!(:interactive_page => page, :question => mc2)
```
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