Importable static builds
When VTK is built static, the vtkpython
executable (and others)
explicitly link and init/import all Python module generated code. This
implies that one can no longer import the vtk
package in the standard
Python interpreter. This change addresses that issue.
Now, we generate a module _vtkpythonmodules_importer
that
loads all static modules but itself can be imported in any Python
interpreter.