More MPRSI2.Player props
MPRIS dbus: added support for properties setters

And implemented the Fullscreen property (Set and Get)
Move the playlist inplementation from music to mediaplayer

This way playlist is also usable by other parts, like mpris
Implemented the full mpris MediaPlayer2.Player interface.

Still to be done: metadata and the PropertiesChanged signal
Implemented metadata for playlist item, used in music/mpris

Also fixed music cover display for albums