Add d3 and Vega libraries.

Vega included in the repo since npm install fails. Including minified because the unminified fails when passing through AM's own minification. (And Closure Compiler for that matter. Weird.)
Slightly smaller font.
graph_flag > embed_flag
Fix range parsing.
Add is_embed default to BaseElement.
Starting port of ChartElement from earlier branch.

Needs to be rewritten given the new modular approach.
Proper extraction of axes labels.
Porting actual charting over.
Scale charts on resize to stay proportional.
Add ChartElement docs to reference.
Merge branch 'feature/charts' into develop