Cleaning Up Ticker Plant Client

This morning I've been cleaning up my ticker plant client - making the ZeroMQ listener of messages smart enough so that when the last listener is removed, the ZMQ socket is torn down thus shutting off the reliable multicast stream of messages that no one is listening for any more. It's a bunch of little details like that - things that will make the code nicer, but not really any less functional for the initial testing and rollout.

It's the "second pass" on the code - adding all those touches you'd expect to see, but aren't required in the first workable cut of the code.