The original MPD server starts at 1. upmpdcli has issues with Mopidy
starting at 0 instead, as 0 is special in its context.
As noone should care exactly what core's TLIDs are, I opted to start
counting both core TLID and MPD songid from 1, instead of just
increasing TLID with 1 in the MPD frontend to get a valid songid. This
also keeps it easier to debug across the MPD/core boundary.
- Split into smaller test cases more or less per command
- Created a BasePopulatedTracklistTestCase with a sensible setUp
- Modified test cases to work with the common tracklist state
- Replaced all calls to tracklist.add(tracks=...) with uris=...
- Test tracklist ordering in more compact way that also gives better error
messages
