Improved login view

Label login as username and mention requested OAuth scopes. /cc #230
Fix for CommentCell. Closes #231
Improved constant usage
Refactoring: Removed unused savingStatus from GHResource
Removed unused KVO from MyEventsController
Handle organization changes in MenuController
Refactoring: Renamed loadingStatus to resourceStatus
Refactoring: GHResource with added changed status
Handle list changes in parent controllers. Closes #229
Added titles for every controller