ScrollBar: Pixel tweak widget-less style

Up and left pointing arrows would look off-center.
Vertical handle would overlap 1px with top button, and miss 1px
to bottom button.

Change-Id: I6fe4ce96e62d864e9d6a7c835067e3c95f51bac4
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>