[xmonad] changes since 0.6

Hi all, I just went through the darcs changelog for xmonad-contrib since 0.6 and added most of the notable changes to the wiki ("notable" = "something someone upgrading from 0.6 to 0.7 might like to know"): http://haskell.org/haskellwiki/Xmonad/Notable_changes_since_0.6 It's not necessarily exhaustive -- please take a look, and feel free to improve descriptions of changes, add notable changes that I missed, and so on. If everyone makes sure that the notable changes THEY contributed are present and described accurately, we'll have an excellent list indeed! Feel free to add notable changes to the core, as well, I haven't gotten to that yet. -Brent