Add AppGyver logo to footer

Add the AppGyver logo and link to the footer. I tried to keep the image scaling similar to the others, I can update as needed. Source logo is here: http://appgyver.assets.s3.amazonaws.com/appgyver_logo.png

Below screenshot of how it looks like in my browser (Chrome)

![screen shot 2014-12-05 at 08 48 32](https://cloud.githubusercontent.com/assets/1642712/5312118/0e36278a-7c5c-11e4-86b2-271ae9db714b.png)