Hibernate cowboy/sockjs processes to save memory

[majek]

Max suggests that we could use hibernate to save memory: http://groups.google.com/group/sockjs/msg/152fc7a4c0718657

[majek]

There are at least three issues with current implementation:

• We do hibernate cowboy websocket process, but we don't hibernate sockjs_session process
• We don't hibernate cowboy xhr processes
• On keepalive (every 25 sec by default) we wake up the ws process and it waits a timeout before going back to sleep.