Add Twitch webhook support

[Bidthedog]

Currently, the front page of the website uses a countdown to "go live" on Thursday nights at 7pm UK time. Whilst this is good, it would be better and more accurate if we used Twitches webhook functionality to switch to the twitch stream on the website.

This may be possible via the front-end, though is authentication is required, we should look at doing this in the back-end, exposing some kind of web socket to the front-end via SignalR or similar.

https://dev.twitch.tv/docs/api/webhooks-reference/#topic-stream-changed