Use Arvo + Open Sans font pairing

People in the user tests complained about the fact that we were using Helvetica for the web application.

This is an alternative, quirky font pairing using Arvo + Open Sans instead. This is just one font pairing alternative and there will be others. This one looks like this:

![screenshot from 2014-05-15 23 52 28](https://cloud.githubusercontent.com/assets/56029/2991247/53cb748e-dc7b-11e3-97b5-c4e5e9310998.png)