Update media-gen.js

Added support for iOS 8 Retina icons & iOS 8 CarPlay

can read about it here

http://makeappicon.com/ios8icon

Icon-Small@3x.png | 87x87 | iPhone Settings for Retina display

Icon-40@3x.png | 120x120 | iPhone Spotlight results for retina display

Icon-60@3x.png | 180x180 | iPhone App Icon for Retina display

Icon-120.png | 120x120 | CarPlay App Icon

iTunesArtwork.png | 512x512 | App Submission

iTunesArtwork@2x.png | 1024x1024 | App Submission