[BColorControl] Various selector bugs
|Reported by:||aldeck||Owned by:||jackburton|
- The invalidation rect was offseted by a few pixels, it could be seen in prefs/Menu color picker.
- Mouse tracking was offseted (vertically) by a few pixels so you could move the red slider while clicking in the blue area.
- Horizontal (left and right) spacing of the selectors wasn't consistent.
The attached patch solves those three issues, although i need some advice concerning binary compatibility since i've modified the class definition.