Full color management for the new color selector

(Awwww yeaaaaah)

Rather than fiddle with garbage internal-VB drawing code, I now render
all elements manually using pdLayers.  This is the simplest way to
guarantee that color management operates as it should.

This commit also fixes issues with selecting colors by clicking the
image preview when color management is active.  Previously we were using
GetPixel on the picture box itself; now we use it on the background DIB
to ensure color-managed results!
Add individual text boxes and picture boxes to color selector

Works wonderfully!

I really do like the GIMP color selector, so I am rather shamelessly
ripping it off in its entirety.  One of the things I like most about it
is that it clearly shows the impact of changing any one of RGB or HSV,
which makes it very simple to acquire colors "like" the one you
currently have, but differing in some singular way.

Next up is RGB <-> Hex, which shouldn't be too tricky... "in theory".
Add hex notation support to color selector

With full support for shorthand entry (of course!).
Assign hand cursor to clickable picture boxes on color selector

This wraps up the whirlwind creation of a custom color selector.  It's
in "workable" state for now, which means I can leave it for a bit to
focus on some other tasks.  (There's still a lot of details left to
tweak/add, but I mostly wanted to implement it to test out color
management.)

All-in-all, not too shabby for an evening's worth of work.