Update iphone and ipad retina icons to new ios7 size

Follows the updated [iOS Human Interface Guidelines](https://developer.apple.com/library/prerelease/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html) for iOS7. 

![screen shot 2014-01-09 at 8 51 16 pm](https://f.cloud.github.com/assets/49507/1884269/f3977164-799a-11e3-8772-c2258c3f1329.png)