COMP: Ensure out-of-source CLI module use Slicer library wrapper

Commit r19677 removed the setting of Slicer_CLI_SHARED_LIBRARY_WRAPPER_CXX
from SlicerConfig by ensuring the use of the wrapper provided
by SlicerExecutionModel.

Then, commit r21592 added the ITKFactoryRegistration library and
also re-introduced a custom cli wrapper without making sure module
externally built would consider it.

This commit set "SlicerExecutionModel_CLI_LIBRARY_WRAPPER_CXX" in
SlicerConfig.cmake to allow module externally built to consider
the Slicer wrapper. It also address the issue discussed in the
following Slicer thread: http://massmail.spl.harvard.edu/public-archives/slicer-devel/2013/012491.html

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22025 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Simplify external project removing CMake 2.8.8 compatibility

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22026 3bd1e089-480b-0410-8dfb-8563597acbee