Add missing icons

[davidpfahler]

To everybody: Feel free to open a separate issue for each of the below. PRs are welcome!

See https://developer.apple.com/library/ios/documentation/userexperience/conceptual/mobilehig/IconMatrix.html for all icons (and splash images).

Missing:

• App Store icon: 1024
• iPhone 6 Plus @3x settings icon: 87x87, Add settings icon @3x size #2
• Toolbar and navigation bar icons: 66, 44, 22
• Tabbar icons: 75, 50, 25 (with different maxima!?)
• webclip icons: 180, 120, 152, 76

First, find out what toolbar, tabbar and webclip icons are and if they should be included here. If so, what should their file names be and how would you include/exclude them when (not) needed?