Add graph drawing w/ sigma.js, forceAtlas2

Rudimentary graph drawing has been developed. Objectives going forward:

 - Make rendering faster. Edges should disappear when zooming out enough, and dense regions have a lot of edges that essentially looks like a grey background but makes rendering very, very slow.
 - Add community detection algo and change the colors of the nodes accordingly
 - Need a standardized version for figuring out where to stop the fdg algo (system energy? predetermined time based on friend amount?)
Merge branch 'master' of https://github.com/socialgrammer/socialgrammer