ENH: Improve performance of node delete

When a node was deleted and it had a display or storage node then the nodes were deleted in a BatchProcess operation.
Entering/exiting BatchProcess is a very expensive operation (many modules re-parse the whole scene and resets displayable managers) and causes the screen to flicker as the layout is refreshed, which is not justified if only a few nodes are deleted.

Changed the code to only apply batch processing if more than 10 nodes are impacted.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24060 3bd1e089-480b-0410-8dfb-8563597acbee