STYLE: Associate a pimpl to qSlicerCLI{Executable, Loadable}ModuleFactory

This is done in anticipation of future tweaking of the factory related
to integration of CTK CLI framework.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23780 3bd1e089-480b-0410-8dfb-8563597acbee