ENH: Adding function to create a new WidgetRepresentation for a module

This can allow the user to "import" a module's GUI into another.
This is particularly interesting for work-flow modules.
The function getModuleGui can grab the existing GUI for the given module,
but the widget representation can only exist in one place. So when using
the GUI in another module with getModuleGui would cause one of the modules
to be empty.

From: Guillaume Sala <guillaume.sala@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22117 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Pass Slicer_PLATFORM_CHECK to inner build

Otherwise, if Slicer_PLATFORM_CHECK is OFF at the superbuild level,
the variable is not defined in the inner build, and automatically set to
ON by SlicerBlockPlatformCheck.cmake

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22118 3bd1e089-480b-0410-8dfb-8563597acbee