Remove deprecated Core APIs

[jodal]

Our Core API is starting to become quite cluttered with old deprecated APIs that we need to remove to make the API easier to use correctly. In additon, removing the old @property APIs will lead to some performance improvements, given the way Pykka proxies currently accesses the properties when inspecting the actor's interface.

Before we can remove the deprecated core APIs, we need to stop using them. Luckily, none of the WebSocket API based clients have ever had access to the deprecated properties, reducing the scope of this a great deal.

• Update Mopidy tests to not use deprecated APIs. See Update tests to stop using deprecated APIs #1083.
• Review Mopidy itself for deprecated API use. For example by removing the deprecated Core APIs, then running automated and manual tests.
• Review all Python-based Mopidy Core API users. See https://github.com/jodal/mopidy-core-api-users for an easy way to search across the source code of many extensions.

Extensions that needs to be updated:

• Mopidy-MPRIS (Stop using Core API properties deprecated in Mopidy 1.0 mopidy-mpris#13)
• ...more extensions identified by the review mentioned above...

Remove deprecated APIs:

• Core
  • uri_schemes property
  • version property
• LibraryController
  • find_exact() method
  • lookup() method's uri argument
  • search() method's empty query returns everything behavior
  • search() method's kwargs argument
• PlaybackController
  • current_tl_track property
  • current_track property
  • state property
  • time_position property
  • get_volume() method
  • set_volume() method
  • volume property
  • get_mute() method
  • set_mute() method
  • mute property
• PlaylistController
  • get_playlists() method
  • playlists property
  • filter() method
• TracklistController
  • tl_tracks property
  • tracks property
  • length property
  • version property
  • consume property
  • random property
  • repeat property
  • single property
  • add() method's tracks argument
  • add() method's uri argument
  • filter() method's kwargs argument
  • remove() method's kwargs argument

[jodal]

We should ignore the items about other extensions above. Extensions will have to cross this bridge themselves.

What remains to close this issue is to:

• Update tests/core/test_playback.py to not use core.tracklist.add()'s tracks argument. (This is also tracked as Update tests to stop using deprecated APIs #1083).
• Remove core.tracklist.add()'s tracks argument.

[jodal]

I've deferred removing the tracks arg to core.tracklist.add() to Mopidy 4.0, ref. #1855.