indicator-sound does not listen for MPRIS Playlist Property changes or PlaylistChanged Signal

indicator-sound checks for playlists once when the player interface becomes available but after that does not listen for ANY Property changes or the PlaylistChanged Signal(correctly at least if it tries, it's doing it wrong. I have not read the source code).

This leads to players that don't immediately have playlists available on interface creation not having playlists displayed. This also leaves players no way to update the playlists even if they are present. The effect then is that new playlists are not added to the list and playlists that have been renamed are not updated in the sound menu's playlist list.

indicator-sound should listen for all Property changes and the PlaylistChanged Signal.

For a working implementation see https://github.com/eonpatapon/gnome-shell-extensions-mediaplayer

For a example of a player that implements the interface correctly(as many players do NOT) see https://github.com/pithos/pithos

Pithos used in conjunction with the extension exhibits the correct behavior. i.e. When a playlist is added, deleted or it's name is changed the changes are reflected in the Playlists list.

This effects all versions of this package that have MPRIS Playlist support.

Full disclosure: I am a collaborator in both the above projects.

If you would like help/guidance implementing the interfaces correctly just let me know.