ENH: #1930 Don't scroll past edges of volumes

Now the arrow keys and mouse wheel events are clamped to the range
of the volumes in the z direction of the slice views like the view
controller's sliders are.  This prevents 'runaway' scrolling and losing
the slice.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22157 3bd1e089-480b-0410-8dfb-8563597acbee