http proxy in front of media server

reasons:

 - we should not give away the identity of a media server
 - media server should not be loaded with multiple upload streams
 - make sure that cache-control and CORS headers are set.
 - rename the chunks every time the same song plays

this will increase memory footprint on master by:

 number_of_rooms * proxy.maxAge / chunkDuration * 30K ~~ number_of_rooms MB

note that number_of_rooms is actualy the number of nonempty rooms. in worst
case every user on application will be alone in his room listening to some emo
music. what a freak.