vtkWrappingPython module has changed to vtkWrappingPythonCore along with
other changes. This commit has corresponding changes for PV to
accomodate for these changes. The following things were done.

- Renamed
  - vtkWrappingPython => vtkWrappingPythonCore
  - vtk_module_classes_load => vtk_module_headers_load
  - {module}_CLASSES => {module}_HEADERS
  - ${module}_CLASS_${class}_WRAP_EXCLUDE => ${module}_HEADER_${class}_WRAP_EXCLUDE
  - ${module}_CLASS_${class}_ABSTRACT => ${module}_HEADER_${class}_ABSTRACT

- Configured the VTK_PYTHON_LIBRARY_DIR in PV instead of VTK

Change-Id: I19112626d3226c7c1bc7145061882bb13244ba36