OpenMW-CS: Deleting an instance requires reload of scene window to show in editor

possibly related to #832 (closed)

deleting can be undone by ctrl-z before reloading.

steps to reproduce: delete an instance in scene window, it doesn't disappear right away, only after scene window is closed and opened back.

instance / object can still be selected so it can be argumented that not disappearing on delete is a feature but not something what is normally expected.

when openmw is launched from inside of openmw-cs the change is instant ie. doesn't require reoload so this is more like a QOL feature.