the color-selection and color-filter-editing GUI stuff; different
toolkits, and different windows systems, have their own notions of color
objects - they may have nothing in common other than the notion that
colors have red, green, and blue values); move it all to the "gtk"
subdirectory for now, and, as we discover stuff stuff that can be made
platform-independent, drag it up to the top-level directory.
svn path=/trunk/; revision=1621
