add CopyWindow module, to support sticky/tagged windows.

This module allows dwm-style tagging (as I understand dwm).  You can have a
given window visible in multiple workspaces.  If it's visible in two
workspaces both of which are visible, a gap will show up in one of them
(which is something that needs fixing in xmonad core).  Also defines a
kill1 which is like kill, but only removes from the current workspace a
window if it's in multiple workspaces.

MetaModule.hs

@@ -25,6 +25,7 @@ import XMonadContrib.Anneal ()
 import XMonadContrib.Circle ()
 -- TODO commented because it requires hs-boot modifications import XMonadContrib.Commands ()
 import XMonadContrib.Combo ()
+import XMonadContrib.CopyWindow ()
 import XMonadContrib.Decoration ()
 import XMonadContrib.Dmenu ()
 import XMonadContrib.DwmPromote ()