Support org.mpris.MediaPlayer2.TrackList TrackAdded and TrackRemoved signals
MediaPlayer2 DBus interface specification describes two signals TrackAdded and TrackRemoved that are emitted when items are inserted to or removed from the player's current list of tracks.
These changes extends the dbus controller module to emit these signals.
Reference: https://specifications.freedesktop.org/mpris-spec/latest/Track_List_Interface.html