Add Sonos unjoin functionality

[lwis]

Description: Additional service to unjoin a Sonos device from a group.

Example entry for configuration.yaml (if applicable):

script:
  group_unpair:
    alias: Group/unpair demo
    sequence:
      - alias: Snapshot Group
        service: media_player.sonos_group_devices
        data:
          entity_id: media_player.lounge
      - alias: Door Bell Play Sound
        service: media_player.play_media
        data:
          entity_id: media_player.lounge
          media_content_id: http://localhost/local/media.mp3
          media_content_type: audio/mp3
      - delay:
          seconds: 6    
      - alias: Snapshot Unpair
        service: media_player.sonos_unpair

Checklist:

If code communicates with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass

[MartinHjelmare]

You can look at the media_player_service_handler in the base media_player module for an alternative way of calling methods of services. It doesn't handle arguments currently though.

[lwis]

I'd like a better way altogether for handling and registering services, it's not very clear which services are available without digging deep into the implementation in some cases.

[balloob]

That sounds more like a documentation issue

[lwis]

@balloob updated the code in reflection to the comments.

[balloob]

Looks good! 🐬