[xmonad] Patch for extending spawnSelected with labels

Hi, I have extended and refactored the spawnSelected function from xmonad-contrib (XMonad.Action.GridSelect). The idea behind this patch is follwing: When using the classic spawnSelected function with long command lines and in combination with defaultGSConfig the label displayed in the grid did not fit into the label. This could be very confusing if two or more entries have the same prefix. For example multiple xrandr entries. regards Daniel