BUG: don't try updating a 2D displayable manager if there is no slice node

This is an invalid condition that can lead to errors being generated
by the rest of the displayable manager code.  The condition that this
checks for happens when a slice view is being created but has not
yet been fully configured (that is, this can be triggered when the
scene is assigned to the slice view, but the slice node has not
yet been assigned; in this case the slice node being assigned will
trigger the needed update).

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23325 3bd1e089-480b-0410-8dfb-8563597acbee
STYLE: remove unused backwards compatibility code

This snippet of code was used during the initial porting of code
from slicer3 to slicer4 but has since been replaced with direct access
to the corresponding items via the regular layoutManager API.

This code also had the unwanted restriction that all Slice View
layout names had to be valid python identifiers (no hyphens or
spaces) which led to spurious syntax error messages for some use
cases.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23326 3bd1e089-480b-0410-8dfb-8563597acbee
STYLE: update to latest CompareVolumes code

Changes style of slice view name.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23327 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: N4ITK changes the image range which can cause problems for images of scalar type short if they fall outside the range

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23328 3bd1e089-480b-0410-8dfb-8563597acbee