Xmonad layout works with relative secondary window sizes

Xmonad layout didn't properly handle screen changes for screens with different y resolutions. Since I didn't want to reset window heights on every screen change I changed the heights from pixels to ratios.

![Selection_003](https://f.cloud.github.com/assets/474896/245391/fe16df14-8a7e-11e2-8be4-2b0065590dc0.png)