Initial websocket implementation

This is initial websocket implementation, nothing really depends on it, only status updates will be slow (update each 5s) if there is some problem (ie. with HAProxy).

I have some trouble with websockets keepalive in my tests, scheduler drops connection after ~10s of inactivity, but worker immediately reconnect. This however introduce potential race condition when running test is displayed exactly in this window (up to 2s), WebSocket message is not passed through, thus updates frequency is not increased.