Added Sonos snapshot feature

[dansullivan86]

Description:
This exposes soco snapshot and restore features.
Enabling the ability to have a Sonos player play something then return to its previous state. My use case is to play a door bell sound effect, but I also envisage it being useful for things like TTS.

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#

Example entry for configuration.yaml (if applicable):

script:
  doorbell:
    alias: Door Bell Automation
    sequence:
      - alias: Snapshot Sonos
        service: media_player.sonos_snapshot
        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://192.168.1.41:8123/local/doorbell.mp3
          media_content_type: audio/mp3
      - delay:
          seconds: 6    
      - alias: Restore Sonos      
        service: media_player.sonos_restore
        data:
          entity_id: media_player.lounge

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If code communicates with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[balloobbot]

farcy v1.1

• D210: No whitespaces allowed surrounding docstring text

[arsaboo]

Wow....this will be great to announce (aka....notifications) on Sonos!

[balloob]

Looks good! 🐬