Use device registry for casts and spotify devices

[fondberg]

This PR replaces #176. #177 got added as well but it should not break anything (tired and forgot to rebase)

[KapJI]

LGTM

[hmmbob]

@fondberg It works for me, yet it does throw errors in the log. But - it works in my use case. Started it twice to verify if this was a single occurrence - happened both times.

Error:

2021-04-11 19:22:02 ERROR (SyncWorker_14) [custom_components.spotcast] No device with id "bf7485e4bdc069dfdaaa748826af2f02" known by Spotify
2021-04-11 19:22:02 ERROR (SyncWorker_14) [custom_components.spotcast] Known devices: []
2021-04-11 19:23:20 ERROR (SyncWorker_11) [custom_components.spotcast] No device with id "bf7485e4bdc069dfdaaa748826af2f02" known by Spotify
2021-04-11 19:23:20 ERROR (SyncWorker_11) [custom_components.spotcast] Known devices: []

Used HA script:

#############################
## Start sleeping music     #
#############################
start_music_t:
  alias: Slaaptijd
  mode: restart
  sequence:
    - service: spotcast.start
      data:
        account: "t"
        entity_id: media_player.hmt
        uri: "spotify:track:5OoSxxxxbP1p7kb1d0SozG"

(device id and track redacted)