Add a simple grid-based layout manager.
Don't stretch the image in UITextureButton().
Uninvert bumpers, fixes hrydgard/ppsspp#1096.
Merge pull request #59 from unknownbrackets/layout

Add grid layout + don't stretch in UITextureButton
Merge pull request #60 from unknownbrackets/pad-fix

Uninvert bumpers, fixes hrydgard/ppsspp#1096