Performance hardening for production

A collection of changes all geared toward improving performance in production, including:
 - Add node-toobusy and 503's if things get too gnarly
 - Refuse to deliver chat messages from non-admins when it's too bad
 - Remove blur/focus
 - Clean up video transport; remove admin scrub controls, fix end-of-video handling and control message permissions
 - Set up to sit behind reverse proxy (e.g. nginx)