PERF: try to import SimpleITK at file scope

Repeatedly importing a library at function scope is less efficient
then  at the module level.

From: Bradley Lowekamp <blowekamp@mail.nih.gov>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22123 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: cast output to int16_t after watershed

Previously the output was being casted to uint16. Some editor effects,
such as the SaveIslandEffect don't behave correctly with this
unexpected image type. The output of the watershed effect is now
converted to int16 if needed.

From: Bradley Lowekamp <blowekamp@mail.nih.gov>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22124 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Revert "COMP: Build SlicerBaseCLI only if VTK is found."

This reverts commit 0692c63d8a06c912258e1f368a9a7c318cc0621a.

This revert is needed bacause CLIs in slicer builds failed to find
SlicerBaseCLI for linking (checked on Mac).

From: Steve Pieper <pieper@isomics.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22125 3bd1e089-480b-0410-8dfb-8563597acbee