ENH: reset editor interface when scene is closing

This avoids situations where the shortcut keys or editor effects are
still trying to respond to scene events when the scene is
in the process of closing.

From: Steve Pieper <pieper@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24474 3bd1e089-480b-0410-8dfb-8563597acbee