Change MPD 'title' to 'track_name' instead of 'track' to avoid confusion

[ZenithDK]

MPD uses "track" to filter on a track number, mopidy converts "title" from the MPD frontend to "track" in the local backend.
Having track mean one thing in the frontend, but something completely different in the backend is confusing.

Edit: Retitled the issue as it was...well, confusing :-P

[jodal]

Mapping between varying terminology in different systems is a large part of the job of Mopidy, sitting between MPD, MPRIS, tags in files on disk and various music services. Mopidy has to choose its own names for things and map it to all the variations. Staying true to MPD will just take us farther away from the other systems we integrate with.

I don't want to change the name fields on Mopidy's models. Though, I'm open to changing the track field in Mopidy's search queries to track_name. That way, title in MPD maps to track_name in Mopidy, and track in MPD maps to track_no in Mopidy.

[ZenithDK]

That was actually what I meant, as we discussed on IRC.
I have no idea how I got into my head that it was track.name and
album.nameI wanted to change, between discussing with you and typing
in the issue :)

I blame too many long days in Korea....

[ZenithDK]

Closed via #557