Convert from ActiveRecord to Mongoid. Require new gems.

Gems
  Add
    mongoid
    rabl-rails
    gon
    bcrypt-ruby

  Remove
    coffee-rails
Create User model on Rails backend.
Modify JSON API specification. Rename app.js, and remove needless routes.

Modify
  GroupBuy API
    Order of properties.
    Add new timestamp properties.

  User API
    Add list of user orders.

Rename
  app.js to unite_to_buy_it.js for disambiguity purposes.

Remove
  Route catchall