* Move Plex->Sonos playback service from integration to platform
* Test against 'native' Plex media_players
* Add Plex to Sonos after_dependencies
* Remove circular dependency
* Raise exceptions in failed service calls
* Add test to forward service call from Sonos
* Additional Sonos->Plex tests
* Fix docstring
* Allow Cast to play Plex media
* Add Plex to after_dependencies, add missing constant
* Extract function from Sonos service to allow media lookups
* Move to non-async method
* Check if media_id exists
* Add test to make codecov happy
jjlawren
Franck Nijhof