Refactor RemoteControlClient.MetadataEditor to move functionality
in new abstract class MediaMetadataEditor, so it can be also
used on the "display" side of the RemoteControl functionality.
Compatibility of these changes has been tested against
existing Play applications which use the RemoteControlClient API.
Move the new constants and method definitions related to the
ratings feature to MediaMetadataEditor. This changes the
yet-to-be-published ratings API, so this doesn't break
compatibility.
Rating feature is handled by the new Rating class with a set
of constructors that handle the different rating models.
Bug 8440498
Change-Id: I9b6dc2204bfc48594bad5cd6449d357f8a485da0
88183e67d4