Add new app icon

![](https://github.com/jasonm23/Phoenix/raw/d9af114f2176c6246fba74a68bf12db8fec8987e/Phoenix/Images.xcassets/AppIcon.appiconset/icon_512x512%402x.png?raw=true)

![screen shot 2014-06-15 at 7 45 23 pm](https://cloud.githubusercontent.com/assets/71587/3280910/a245eaa0-f485-11e3-983d-eb4df14ff52d.png)

![screen shot 2014-06-15 at 8 07 06 pm](https://cloud.githubusercontent.com/assets/71587/3280911/a2473ee6-f485-11e3-92bd-a2fb9b8f2601.png)