Add gRaphael charting library

Summary:
I typed up like 30 pages here and then got my soul crushed by T895, but here's
the summary:

I looked at several charting libraries. There aren't very many that seem to be
any good and have an open-source license.

I also want the charts to be scriptable in JS so we can add good interactivity
where appropriate.

Raphael is an SVG drawing library which seems very solid. gRaphael is a charting
library on top of Raphael that is a lot less solid, but seems kind of OK.

Overall, I think this selection gives us a lot of flexibility, although we'll
have to pay some costs up front. I'd rather do that then get limited later,
though.

That said, I'm open to other suggestions here if anyone has experience or wants
to take a different stab at researching things.

This is largely for @vii and D1643.

Test Plan: Created a basic, fairly OK chart (see next revision).

Reviewers: btrahan, vii

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1654