[Dillo-dev] ui colors again

http://www.dillo.org/test/color_themes.diff I was just playing around with making themes selectable. I typed in some color themes that Jorge has suggested, and typos in them are possible. I tried using some of the fltk color indices for our tab colors and button highlight color in order to make the code more uniform, placing the #defines in prefs for lack of an obviously good location. It has code to fix the deactivated icons when the background color changes, but I'm still not very pleased with it.