Introduced an unhideall function that can be used to reveal all hidden client in the current view.
Added a change to unmanage to avoid changing the window state from IconicState to WithdrawnState when the window manager stops managing windows (which happens when restarting).
Previously a hidden window would disappear when restarting dwm because:
- when hidden the window would be unmapped and having the window state of IconicState
- when restarting the window would remain unmapped while the window state would become WithdrawnState
- which would prevent the window from being picked up by the scan function when the window manager starts
