STYLE: Refactor SlicerWizard into Python modules

Replace Scripts/SlicerWizard.py with a very short script that merely
imports the main wizard class, intantiates it, and calls its execute()
method. Move the code into two new Python module files in a
subdirectory.

This will allow for better scaling as we add features, by allowing us to
create additional modules as it makes sense, rather than needing to
encapsulate everything in a single monolithic script file.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22950 3bd1e089-480b-0410-8dfb-8563597acbee