Fix Scrollbar arrow button alignment.

The arrow symbol on the right and down buttons was off by one pixel.

Because of the resurrected FakeScrollbar in the Appearance preflet I had to
change this code in two places, which makes me unhappy. This needs to be pulled
into BControlLook.

Fixes #9104.
Use be_control_look for BScrollBar and FakeScrollBar.

Remove all code which checks for be_control_look being NULL.

Also fix the DrawArrowShape method in be_control_look so the arrow is aligned,
as per the previous commit. In addition the code to offset the arrow when the
scroll button is pressed was unnecessary.

There is still some room for improvement, and I am not happy with the
BControlLook behavior here, as noted in some TODOs.
Removed unused colors from BScrollBar Draw.