MessageProcessor: Use raw zmq socket

makes transition to CurveZMQ easier

removes some cron and timeout functionality, will be re-added when required
It will call `ProcessCron()` just before it waits for a new request. 

When no requests are processed, no cron tasks are processed as well. 

I'd rather call it periodically it in a separate thread and use a mutex to prevent simultaneous execution of `ProcessCron` and `ProcessMessage`