Memory platform counters

Adding summingbird counter support for the Memory platform.
hm, I think this can work in scalding, but I am not sure about storm. The contract here is that the users create Counter objects, increment them in their job and then look at the final value after the job is done. With scalding, we can query the hadoop counters, but with storm, I don't see how it would work. Right now we look at storm counters in the viz graphs for the running topology.