Added master layout

This layout has one master window which takes up half the screen. All other windows are laid out using the column layout on the other half of the screen.

Feel free to reject this if it doesn't fit with what you're trying to do going forward. This is the first Idris I've ever written and I haven't used XMonad before. I just got interested in trying out Iridium after your Strange Loop talk and found that I really wanted this kind of a layout.