[Sprint: 38] XD-2107&1048: --nameExpression for metrics & --incrementExpression for agg-counter

I see. Overall the changes here are reducing the repository to nothing more than accessors for the RichGauge instance (and doing so in a way that is not thread safe - which needs to change before we can merge this). It is no longer a "service" in its own right. That is a pretty significant break of backwards compatibility if anyone was using these as services. I'm pretty sure @markpollack had the intention of that representing an API for counters that was not exclusively available through the use of MessageHandlers, but I'll let him comment on that.