ColorControl: Implement keyboard navigation

Implements enhancement described in #9819

This feature works pretty much as it did on BeOS R5.

When you focus on the color control, the border is drawn blue and
the dot on the red ramp draws as an outline to show that it is
selected. You can push the up and down arrow keys to navigate to the
previous and next ramps respectively and can push right and left to
increment and decrement the color value of the selected ramp.

Clicking on the control no longer gives it focus.

In BeOS the left and right arrows would increment and decriment by 5,
on Haiku they increment and decrement by 1, but, by holding down the
key for a second or so the increment value increases to 5 allowing for
both course and fine adjustments.

On a technical note I split the int32 fFocusedComponent member variable
into 2 int16 member variables, fFocusedRamp and fClickedRamp. I did this
because I needed an entra variable, and can't  change the size of the
class without using up another reserved member variable slot. int16
should be more than enough for these variables as they store an index to
the currently focused or clicked on ramp (0-3). Please someone chime in
if this is not okay for FBC in some condition I didn't think about.