Improved colorbutton

Currently, the colorbutton is very cumbersome to skin, because it uses statically colored button images and a colorized overlay image, which is scaled differently than the button images.

This branch simplifies the colorbutton by directly colorizing the button images and getting rid of the overlay. As a result, its look and feel can more closely resemble a radiobutton (which it is a subtype of).

Existing skins have been updated.