Added command ml_sonos_playlists.

Uses MLSonosPlaylist from https://github.com/SoCo/SoCo/pull/114

I couldn't get it to fully work right now, but I couldn't get any of the other ml_{tracks,albums...} commands to work now either, so I'm not sure if that's a a bug somewhere else or if it's my setup failing. The part that broke was 'ml_{pick any type} % add 10' , a simple 'ml_sonos_playlists %' search however works. I can open a separate issue for this though.