STORM-312 : add storm monitor tools to monitor throughtput interactively

This cmd line tool 'storm monitor' will use Nimbus.Client to get throughput information from Nimbus Server.
1)One can specify topology's name, component's name to monitor it's throughput interactively.
2) It will statistics 'emit' or 'transferred' throughput in a given time window and print it in a given time frequency
The implementation will be much like yahoo's storm-perf-test (http://yahooeng.tumblr.com/post/64758709722/making-storm-fly-with-netty)
Since we're already introducing changes in Clojure, how would you feel about implementing some (or all) of this in Clojure? I feel like MetricsState and Poller are bad fits for Java, and that it could be a great place to use Clojure's concurrency features, such as an [agent](http://clojure.org/agents).