Move the Python wrapping to the end

This moves the Python wrapping to the end of the build process, using
the information exported by the module files.

Change-Id: I711382f79fc1fdb15cd80c87f55dd2f97a2c5cd8
Complete the rename of vtkWrappingPython

The vtkWrappingPython module is now vtkWrappingPythonCore.

Change-Id: Id3a1f32bc4a21e80181ac45d23ab3457c40d4eae
Rename vtkModule-Classes.cmake to vtkModule-Headers.cmake

After discussion on the mailing list we decided that this better fits
the purpose of the file which is intended to export a list of all
headers in each module along with their properties.

Change-Id: Icd0dd5938427621dfe6a871ddaa94db8f063081f
Fixed Tcl wrapping, and some special classes

Added some code to handle .txx files more elegantly, so that they can be
listed as source files and the corresponding header file found. Moving
away from WRAP_HEADER and using WRAP_SPECIAL (which largely means wrap
in Python at this point in time when used in conjunction with
WRAP_EXCLUDE).

Change-Id: I51447090d1b351d03474a5d4972eab7a0d3f9f78
As discussed in review - rename CLASS->HEADER in modules

This (hopefully final commit to this topic) renames the variables to
HEADER/HEADERS rather than CLASS/CLASSES. The function is also renamed
from vtk_module_classes_load to vtk_module_headers_load but performs
essentially the same functions. Updated the documentation to reflect
these changes.

Change-Id: I6f44971a865c6788c16c6311f6704f21612a083b
Merge remote-tracking branch 'origin/master' into python-wrapping

Change-Id: I0a91be1e4b8dbe0a0c2ecb82d26251385d1f0b06
Merge topic 'python-wrapping' into master

98acc25e Merge remote-tracking branch 'origin/master' into python-wrapping
524f23d4 As discussed in review - rename CLASS->HEADER in modules
9c9c3ebd Fixed Tcl wrapping, and some special classes
643aa039 Rename vtkModule-Classes.cmake to vtkModule-Headers.cmake
a9b37f20 Complete the rename of vtkWrappingPython
34903fe1 Move the Python wrapping to the end