GRAPHICS: Cleanup of old code
SDL: Cleaning up some code
VARIOUS: Fixed up some unnecessary linebreaks...
SDL: Cleaned up clearOverlay();
GRAPHICS: Refactored code for rounded squares

This commit also disabled the border-color, instead relaying on the bevel,
since that code will be changed soon anyway
GRAPHICS: Gradient effect on bevels for rounded buttons (AA only)
GRAPHICS: Removed hardcoded offset