X.H.DynamicBars: support per-monitor cleanup
X.H.DynamicBars: support per-monitor cleanup

Add functions to allow cleaning up only screens which disappear. This
works better where killing the statusbar for a specific screen is
possible. The old way is still relevant for setups which do not have
such a method (e.g., safeSpawn xmobar/spawnPipe xmonadpropwrite).

f1u77y/xmonad-contrib,f1u77y/xmonad-contrib,xmonad/xmonad-contrib,xmonad/xmonad-contrib