MessageProcessor: Use raw zmq socket

makes transition to CurveZMQ easier

removes some cron and timeout functionality, will be re-added when required
@mhamrle 

Cron needs to run also if no messages are sent at all, for recurring payments etc.

Not sure how you intend to use zmq_poll for a cron, since cron and zmq are completely independent things.
We are already using zmq_poll [here](https://github.com/Open-Transactions/opentxs/blob/develop/src/ext/OTSocket.cpp#L224].