Desktop blur of applications in one execution step

 * the -b parameter now needs a value called the app command line
 * upon receiving this command, desktop is blurred, app launched synchronously,
   when the app finishes the desktop is restored to original state.
 * example: kdesk -v -b "lxterminal --command=\"/bin/bash -c 'ls -l ; sleep 10'\""
   will popup a lxterminal listing your directory contents for 10 seconds with blurred background
   then quit and return UIX to original colors.
 * if a second blur requests comes in, it will unblur the desktop and quit.