Basic statistics page (ready for synthesis stats)

This page is [available for review](http://devtree.opentreeoflife.org/about/statistics) on **devtree**. It currently has just synthesis stats. Once we have the second stats file `phylesystem.json` to play with, it will be quick to copy the same behavior in the bottom section.

_**NOTE** that the stats file used here is based on the one @pmidford provided, but I added two bogus profiles from "previous months" to work out the UI._ This file (`ot16:/home/opentree/repo/opentree/webapp/static/stats/synthesis.json`) should of course be replaced with real data as it becomes available.
 
I've built a UI to walk through the history of stats profiles, since this will clearly be a requirement. I also added sparklines (tiny plots for each statistic, built on-the-fly using the Google Charts API) as a nod to showing trends.

This branch adds [moment.js](http://momentjs.com/) for parsing ISO-8601 dates from our stats files. I've added this to the **About > Licenses** page in this branch.