HaikuDepot: Exract RatingView into its own source and header
HaikuDepot: Extracted SharedBitmap into its own files
HaikuDepot: Organized source into sub-folders
HaikuDepot: Split generic and specific UI classes

* Also fixed placement of PackageManager which I must have
  dropped into the wrong folder by accident.
HaikuDepot: Allow RatingView to be wider than MinSize().
HaikuDepot: Add actual rating to RatePackageWindow.

Implemented SetRatingView based on RatingView. It previews the rating
when hovering and makes it permanent when clicked.
HaikuDepot: Define StringList type for convenience.
HaikuDepot: Put supported languages into a StringList

* Added TODO to retrieve the list from the web-app, there is already an
  API for it. For now, the hard-coded list matches the web-app's and the
  next change in this regard will be to support any known language.
* Make the list accessible.
HaikuDepot: Allow to set the rating comment's language.
HaikuDepot: Handle BMessage for rating comment language