About UI updates

Updates to the About page UI, including font changes, retina logo update (the old app didn't have retina RubyMotion and Twitter logos), and adding Mohawk & Iconoclast logos to the bottom.

![screenshot 2014-04-08 16 02 05](https://cloud.githubusercontent.com/assets/139261/2649098/f7d413a4-bf5e-11e3-8ab5-24f8e906c3bb.png)