GApplication now has a palette. This palette contains all the system
theme colors by default, and is inherited by a new top-level GWidget.
New child widgets inherit their parents palette.
It is possible to override the GApplication palette, and the palette
of any GWidget.
The Palette object contains a bunch of colors, each corresponding to
a ColorRole. Each role has a convenience getter as well.
Each GWidget now has a background_role() and foreground_role(), which
are then looked up in their current palette when painting. This means
that you no longer alter the background color of a widget by setting
it directly, rather you alter either its background role, or the
widget's palette.
I added focus rects to these widgets because I had just started working on
focus support and I was excited but it doesn't really make sense for these
things to have focus rects. :^)
While I was here I also optimized the repaint code to only update the edited
glyph in the glyph map when editing its pixels.
