Added documentation and testing to vtkPythonAlgorithm.

Also added a Python superclass to make algorithm
development easier.

Conflicts:
	Filters/Python/module.cmake

Change-Id: I23fbee8b39d10c4fa75faa7704153a8d58df9445
pythonalg: use keyword arguments rather than members

Change-Id: Ib3bdb7fcadb08907b0243da45e78d2e983437fdc
pythonalg: raise an error in RequestData by default

Change-Id: I5eeaba72d9e9869b6bc3b8190d5888671f3bf1d0
Merge topic 'python-algorithm-2' into master

adf3b4d8 pythonalg: raise an error in RequestData by default
0b1ca3a0 pythonalg: use keyword arguments rather than members
4787c7a4 Added documentation and testing to vtkPythonAlgorithm.