[mpris] MPRIS v2.1

[Conor Curran]

Hi Lennart,

Honestly I am uncertain of the usecase for the Tracklist API, if Mirsal 
and Alex can see the obvious correlation between the two then a change 
of name would be the most sensible thing. I do think however playlist as 
a word leaves no ambiguity. Its straight forward as to what it refers 
to. Tracklist is more generic which leaves some room for interpretation. 
AFAIK all players use the word Playlist to refer to custom collections 
of tracks.
> Why not add HasTrackListEnumerator akin to HasTrackList?
>
>    
Good idea.
+1

Conor