Configurable option to mute audio by default

[charonfaustinus]

I'm always frustrated when people put unrelated loud music on their video for no reason.
I always need to mute every video when I go through the feeds.
Maybe have server side configurable option to mute audio by default?

[Znuff]

#166 might help with that issue, it will also remember if you turn down the volume all the way to 0 (so, muted) on all videos