Multi-streamer QOL improvements

[Belchy06]

This PR adds a few QOL improvements to the library, specifically for the case where the are multiple streamers.

• The streamer selector is now updated on stream start to show you which streamer has been selected
• The PreferSFU toggle is now functional again
• Changing the streamer selector during a stream destroys the current peer connection and connects to the newly selected streamer (UE doesn't support re-negotiation so this is currently one of the only options)
• Auto subscription on only one streamer has moved from cirrus to the frontend (tested and maintains backwards compatability).

The frontend now has an order of operations when checking which streamer to subscribe to. It is as follows:

• If there's a single streamer, subscribe to it regardless of what's in the URL
• If there's an SFU AND the PreferSFU toggle is on, subscribe to it regardless of what's in the URL
• If there's a streamer ID in the URL AND this streamer is connected to the signalling server, subscribe to it
• If none of the above conditions are met, no stream is subscribed to

[lukehb]

All commented have be addressed. Landing.