Add Support For Ganglia Metrics

Apache Ambari (http://incubator.apache.org/ambari/index.html) uses Ganglia (with RRDs, not Graphite) for its metrics, and we were very interested in upgrading to using your fantastic Cubism visualization for said metrics across all the hosts in a Ganglia cluster.

I wrote the new gangliaWeb.js Cubism source (and have it working nicely), so I figured I'd give back to the community - feedback would be much appreciated, and I'll be happy to make improvements as you might see fit.

Using GangliaWeb as a source means users of Ganglia get to work with both RRDs and Graphite as the storage engine, for the price of one.

Thanks for the great foundation, Mike!

/V

P.S. Prospective early adopters should note that this won't work with GangliaWeb until https://github.com/ganglia/ganglia-web/pull/110 is committed.