CORE-5313 Rating comments now optional.

Added an AppCommentCell with associated AppCommentSelectedEvent, handler interfaces, and appearance.
Added a Comments column in the App listing grid using this new cell.
Updated the AppsViewPresenter to now handle adding and editing App comments.
The Rating cell now only updates user (and avg) ratings.
Refactored some of the AppUserServiceFacade App comment method names and signatures, and added a rateApp method.
Refactored the rating and comment endpoints to take the App's wiki url, and the service facade now parses the URL to get the confluence wiki page name.