Migrate to alternative charting library

[gapple]

Google Charts is somewhat inflexible, and there is additional information that might be helpful to place on the charts that it is just not capable of.

Probably minor, but it also doesn't seem to cache in the browser well, with the dynamic loader, and charts can't be rendered when developing offline.

D3.js: https://github.com/mbostock/d3/wiki/Gallery