[xmonad] NamedScratchpad use case patch

Hi, This is a patch to make easier use of NamedScratchpad with the DynamicLog pretty printing capabilities. It took me a little while to figure out why the examples given in IndependentScreens were not working when using NamedScratchpad. I knew I had to use namedScratchpadFilterOutWorkspace but it was not obvious how to d'o so. Hopefully this patch helps. Regards, Nicolas