Proxy Graphite requests through Descartes

This has the benefit of avoiding CORS setup and troubleshooting. Unfortunately, it comes at the cost of latency thanks to blocking requests through Thin server. Casual tests revealed that a page of twelve (12) non-proxied graphs would load in approximately 400ms. The same graphs, loaded through the Thin server acting as a proxy, finished loading between 1400ms and 1800ms, with some taking as long as 2200ms.

In order for this to be a feasible design we'll have to consider moving to Unicorn for the extra threads. My initial stab at this was unsuccessful, unable to get Sequel connections loaded properly in the thread pool.

cc @gorsuch