ENH: Hide symbols in the CLI modules.

Update SlicerExecutionModule to incorporate
Slicer/SlicerExecutionModel@8d607ff93a3be76274d9cedfb9f1148a6cdb6968
which hides non-CLI symbols so only ModuleEntryPoint, etc. are available in
the CLI shared libraries.

This results in the following lib/Slicer-4.5/cli-modules size improvements,
Slicer start-up time improvements, and reduction in
GradientAnisotropicDiffusionLib symbols:

                     MinSizeRel: no hidden | MinSizeRel: hidden | Release: no hidden | Release: hidden
                     ---------------------------------------------------------------------------------
size (MB)             104                     89                   119                 107
start-up time (sec)   20.2                    16.2                 20.0                18.7
example cli symbols   2593                    328                  2342                322

From: Matt McCormick <matt.mccormick@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25004 3bd1e089-480b-0410-8dfb-8563597acbee