Gives Firefly the ability to have graphs with stats from multiple data sources

This patch gives firefly the power to poll multiple data servers for data, allowing for graphs with mixed data servers and data sources.

This doesn't completely close #7, since there's still a small bug in StatMonsterRRD; I'll fix that in a subsequent pull request.

I'm really not a good Javascript programmer, so I'd like your best criticisms so that I can get better.