[xmonad] First steps (not only words)

Breaking gwern's suggestion this is my second mail today :) The way to implement some of my suggestions? * Clean XMonadContrib of duped functionality modules * Reviews XMonadContrib in search of dupped/common-used code * Move this code to another contrib module, and maybe implement a better interface over it * Write good docs about the new module, it will be the base from new modules to come * Maintain this module in partial-stable situation (limitting commits) * Move some functionality of this module to core With these steps we can assure less breakage fom updating contribs, and that will be more easy to write new modules because there's a common codebase written and approved by core devels. bye!