Add current_user action in the Application Controller

Returns session[:user_id]

Added for readability
Finish (for now) refactoring of Transaction model and unit tests
Refactor PaymentMethods Controller, Model, Unit Test

Remove the custom save action that added the user_id, instead
adding the user_id in the controller right before the normal
save.

Remove the custom save tests.

Replace session[:user_id] with current_user helper method in
the controller.

Remove default comments in the controller.
Clean up PaymentRecipient Unit Test
Refactor PurchasePurpose Controller, Model, Unit Test

Remove custom save action that added the user_id, instead adding
the user_id in the controller.

Remove custom save test.

Remove standard comments from the controller.

Remove json responses from the controller.
Refactor PurchaseCategory

Remove the custom save action from the PurchaseCategory model.

Clean up the tests - make examples read better
Refactor Subscription Model, Controller, Unit and Integration Test

Model:
  Remove unused actions:
    subscription_details
    set_cycle
    set_name
    set_end_date

  Refactor create_subscription to take the transaction object
  instead of an options hash.

  Add a self.user_subscriptions action to display only the
  user's subscriptions

Controller:
  Remove unused details action.
  Remove standard comments
  Remove unused json responses
  Set index to only display the user's subscriptions

Routes

  Remove standard comments.
  Remove subscription_destails route

Unit Test

  Clean up before action.

Integration Test

  Clean up before action.
  Clean up create_a_new_subscription action.
  Remove unnecessary tests.