Setup overview page

This PR creates an overview webpage that shows the last 10 charges submitted and top 10 accounts by lifetime value. It also allows the consumer to get the lifetime value of any account given an account ID. It's based on the [Foundation](http://foundation.zurb.com/) front-end framework.

If we'd like to keep going with this the next step would probably be to add some integration testing but off the top of my head I'm not sure what the python equivalents of cucumber and selenium are. We could also look at adding pages for list accounts/charges that have longer tables that could be sorted and filtered. Search functionality also wouldn't be that hard to add but would probably require some other systems to do right (elasticsearch, solr, etc.).