Merge changes from topics "sessiontoken2_simpl", "move_binder2",...

Merge changes from topics "sessiontoken2_simpl", "move_binder2", "mediaitem2_updatable", "session2_sendcustomcommand"

* changes:
  MediaSession2: Simplify constructor of SessionToken2
  MediaSession2: Move binder interfaces into the updatable
  MediaSession2: Move MediaItem2 to updatable
  MediaSession2: Implements sendCustomCommand()