Making vtkPythonCalculator easier to read.

Making vtkPythonCalculator use a python module calculator.py instead of inlining
all the Python code which made it difficult to update the python code.

Conflicts:
	ParaViewCore/ClientServerCore/Default/vtkPythonCalculator.cxx

Change-Id: I9fac55b45be18d973c5f9a679a07734b199f4483
Reapply f54399abf after cherry-pick.

Change-Id: Ie0df5f8a1a1b06179c6248fbe5aa7ef3cf9d62e0
Fixup PythonCalculator and ExtractSelection with composite DSs.

Change-Id: Iadcf65f7d77e3da728e8fc19c460ff3a5c3368fa
Merge topic '14565-composite-queries' into next

996eefb2 Fixup PythonCalculator and ExtractSelection with composite DSs.
557286d4 Reapply f54399abf after cherry-pick.
439006c9 Making vtkPythonCalculator easier to read.