Window padding 2

Take two, free of xcode badness, much cleaner solution than the original.

Thoughts?

The bug where Amethyst won't resize windows a small amount is still present in this version.

Steps to reproduce, launch Amethyst with a window padding of 0, layout a normal tall layout with 3 windows. Switch window padding to 10 and relaunch amethyst. Expected, windows are laid out with padding. Actual, windows shifted but not properly sized. Workaround, switch between two layouts