Removed error handling from User.subscribe method. Any errors raised will be handled at the controller level.
Changed the User.subscribe method. Moved the code that checks if the feed is already in the database to a new private method, User.subscribe_known_feed.
Simplified the User.subscribe method. Moved the code that fetches and subscribes to the feed if it's not yet in the database to a new private method, User.subscribe_new_feed.