Deprecated Core APIs to remove in next breaking release

We have a small set of Core APIs emitting DeprecationWarning in our source code now:

• core.playback.play()'s "tl_track" argument is deprecated since 3.0, use "tlid" instead.
• core.tracklist.add()'s "tracks" argument is deprecated since 1.0, use "uris" instead.
• core.tracklist.eot_track() is deprecated since 3.0, use tracklist.get_eot_tlid().
• core.tracklist.next_track() is deprecated since 3.0, use tracklist.get_next_tlid().
• core.tracklist.previous_track() is deprecated since 3.0, use tracklist.get_previous_tlid().

We should stop using these APIs ourselves as soon as possible, and remove them in Mopidy 4.0.