Youtube Refactoring

PivotalTracker Story: https://www.pivotaltracker.com/story/show/69074352

* Refactored `Youtube` into `YoutubeVideos` and `YoutubeHelper`
* Plan to move all the API calls to background job to improve performance in a later pull request.

1. `app/controllers/projects_controller.rb` - Changed the way to youtube videos are fetched to use the new YoutubeVideos.
1. `app/controllers/users_controller.rb` - Changed the way to youtube videos are fetched to use the new YoutubeVideos
1. ` app/helpers/application_helper.rb ` - Removing unused and useless methods.
1. `app/helpers/users_helper.rb` - Everything related to YouTube moved to `YoutubeService` and `YoutubeHelper`.
1. `app/helpers/youtube_helper.rb` - Contains methods used to fetch a user's youtube related information when he syncs with youtube.
1. `app/models/project.rb` - Added a members instance method, to remove duplication throughout the app.
1. `lib/youtube_videos.rb` - This YoutubeService encapsulated all the functionality for fetching both user videos and project videos.
1. `features/project_pivotal_stories.feature` - Fixing the project pivotal tracker stories feature to stub out the request for youtube on the project index page.
1. `features/step_definitions/youtube_steps.rb`, `features/tabs.feature` - Switch to the new YoutubeService.
The last two are expectations to make sure that the correct thing gets assigned. The first two are two make sure that the API gets called and to stub out the response.