Add voice chat

WebRTC allows us to add voice chat into the game. This wasn't done earlier, because I had to provide own servers and the support was poorly at that time. But some years later I think its now time to add this and do all the groundwork that's needed. Some key features the voice chat has to supported:

- Automatic join voice chat if the player enters the lobby
- Auto mute player if the browser tab goes into background
- Auto mute and deafen player depending on the chat settings
- Highlight speaking player in game
- Highlight muted player in game (e.g. 🔇)
- Still allow voice chat!