Started adding round color picker.

However, I don't yet know enough to finish it, and I'm currently off-line, so I can't look it up.  So I made these changes safe (or commented 'em out) and I'll move on.
user highlight in the color picker.  rendering the user selection in the color picker (barely).
Optionally using color picker.  Toggling between color picker and faders using a 'segmented control.'
Color picker changes faders.  Made the color picker update the text labels and the fader positions.
Cached color-picker image.  The color-picker background therefore draws instantly whenever we load the color-picker page.  Before, it was re-rendering every pixel each time the page loaded.