Implement MediaPlayer2 interface of MPRIS

https://bugzilla.gnome.org/show_bug.cgi?id=702866
Implement MediaPlayer2.Player interface of MPRIS

https://bugzilla.gnome.org/show_bug.cgi?id=702866
Request album, duration and thumbnail metadata in grilo queries

https://bugzilla.gnome.org/show_bug.cgi?id=702866