Investigate whether the SocketIO transmitter is "fair"

[jackjansen]

If multiple streams are multiplexed over socketIO it is important that the sender does this fairly, and doesn't first transmits everything available for stream 1, then for stream 2, etc.

Because if it does that and the streams need to be synchronised on the receiver side this would lead to ever-increasing delays (as everything waits for the "unluckiest stream").

@troeggla if you don't have time to look at this assign back please.