Change the border resize rectangles to be narrower and only extend
inside the window not outside. Most window managers just seem to use
the border decoration area for starting resizes which is often just 1 pixel
wide but as a compromise the width is now 2 pixels (before it was 10!).
The rectangles are now placed symmetrically within the border and window.
This seems to work ok with PositionStoreFloat for the Bluetile config.
