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

This is what I've been trying to say all along. But note that even then I was mistaken, as 
1) the handler is now not "threadsafe", but before, it was the repository that suffered from the same problem. We've just shifted the problem IMHO
2) more than "threadsafe", what we want is "distributed-safe" I believe, and this gets much more complicated