Chromecast support

[shish]

It would be pretty neat if:

• user visits karakara.uk and logs in using the browser2 interface on their phone
• they click the "cast" icon
• the player2 interface appears on their TV, logged into their room, reacting to their phone's commands

There is a proof of concept for this in the chromecast branch. TODO list:

• make the "cast" icon neatly integrated in the browser2 menu bar
• send a chromecast "play this media ID" command from browser2, using the queue name as the media ID
• have player2 listen for "play this media ID" commands, set the queue name when it receives one
• find some way to send chromecast keep-alive signals (the client library will kill the app if it goes 60s without a google command - but we do all of our commanding via MQTT, so google thinks nothing is happening) (Can we tell the library to play a silent 10 second audio track on infinite loop?)

Notes:
Unfortunately we can't tell chromecast "go to https://karakara.uk/player2/?queue_id=blah" - we have to register an app with google's developer program (I did this, our app ID is 05C10F57), then tell it "open app 05C10F57", then it goes to google's database and sees that "app 05C10F57" = "https://karakara.uk/player2/". Only after it has finished loading the generic player2 page, can we then send it a command telling it which room to join.

UPDATE: For player3, the app ID is 0FDED252

https://developers.google.com/cast/docs/web_sender/integrate
https://developers.google.com/cast/docs/reference/web_sender/

https://developers.google.com/cast/docs/web_receiver/basic
https://developers.google.com/cast/docs/reference/web_receiver/

Launch chromecast debugger from chrome://inspect/#devices

[shish]

Chromecast TV HD/4K support h265, so I have ordered one of those to test with, maybe it'll support smooth CSS animations too