New highcolor! :)

The drawing's the same, but now it pays attention to all the widget's
colorgroups and can automatically generate new gradients that don't match the
standard palette. This is needed for the extended color schemes, which let you
set custom colorgroups for just about everything :)

You can see it work right now with kcalc's custom buttons
(http://www.mosfet.org/kcalc-newhighcolor.gif). I'm still getting the new color
scheme widget done :P

Also fixed the checkbox bug ;-)

svn path=/trunk/kdelibs/; revision=68674