Refactoring CMake code for Python modules.

Adding some infrastructure to properly handle vtk-modules that are
simply Python packages or modules.

This change adds API in vtkModuleMacrosPython to manage all the building
and installing of Python modules and packages minimizing the confusion.

Past attempts fix six.py, vtk/web etc. failed to distinguish cleanly
between a Python package and a module which was resulting in directories
being "unwrapped" on install (e.g. with autobahn) or py files getting
put in subdirectories (six.py).

This also manages installing on "vtk/web" package under the "vtk"
package cleanly. For that we needed to move the *.py files in Web/Python
into a subdirectory reflecting the targetting package structure.

Change-Id: Ic251c34418b07838e5bb483c2b02b12004f17632
Merge remote-tracking branch 'origin/master' into fix_python_packages_and_modules_in_vtk_modules

* origin/master:
  Replaced buggy and redundant implementation of GetRGBPoints()
  Refactor parts of vtkLookupTable
  Removed unused types and member variables, fixed formatting
  Add wrap hints for vtkPoints2D and vtkRenderWindow.
  Properly handle WriteAllTimeSteps = false for vtkADIOSWriter
  Expose WriteAllTimeSteps as a setable parameter for ADIOS
  Remove leftover debug messages
  web: print the traceback from errors as well
  web: support Image from PIL in testing
  dashboard fixes and debug leak
  Adding in a filter to append structured grids together.
  fix some warnings
  removed unused includes

Change-Id: Icf1abae2e56d62a76e07cb90aa3824aa338d0c3a
Merge topic 'fix_python_packages_and_modules_in_vtk_modules' into master

23cf829e Merge remote-tracking branch 'origin/master' into fix_python_packages_and_modules_in_vtk_modules
dc8280bd Refactoring CMake code for Python modules.