Persist stream volume and mute settings per user across stream sessions

Stream volume and mute preferences currently appear to be tied to the current stream/voice connection rather than permanently to the user who is streaming. This means that when someone stops streaming, reconnects to voice, starts another stream later, or enough time has passed, I may have to set their stream volume or mute state again. For example, if I usually keep a specific user's streams at 30% volume or muted, I would like Fluxer to remember that preference the next time I watch a stream from that same user.

Persist screen share / stream audio preferences per streamer user, instead of only for the current stream connection. For each user, remember:

• Stream volume
• Stream mute state

These preferences should survive:

• Closing and reopening their stream
• The streamer stopping and starting a new stream
• The streamer leaving and rejoining the voice channel
• Leaving and rejoining the voice channel as a viewer
• Restarting the Fluxer client

The saved preference should remain until the viewer changes it again or explicitly resets it.