optimize images with ImageOptim

Ran ImageOptim on app/assets/images "Saved 6.7KB out of 144.KB. 4.7% per file on average (up to 51.8%)
![screen shot 2013-12-21 at 1 02 55 pm](https://f.cloud.github.com/assets/1312687/1796515/ba36b2f4-6a72-11e3-80b4-7b3a2fe3a18e.png)