Clean up Python CoProcessing script logic.

This cleans up the logic in Python CoProcessing scripts and the export wizard.
Creating new Python modules (coprocessing, cpstate and cpexport) that are now
used instead of embedded codes. CoProcessing Python code has been revised to not
heavily rely on global variables and secret code stubs.

Change-Id: Ie36913fc2337ca4897d022d07c80f7912428d594
Removed vtkCPPythonProcessor.

Removed vtkCPPythonProcessor. Now, vtkCPPythonScriptPipeline initializes Python
when the first pipeline object is created.

Change-Id: I3349cc0e6aec3c763e0a351b419435f42be35aac
Setup default sessions during initialization.

ParaView initializes without any session active. Since we need an active session
always and it's always a built-in session, set one up during initialization.
This ensures that the logic for setting up session defaults doesnt cause
segfaults i.e. CoProcessingTestPythonScript passes.

Change-Id: Ie31b3f1799324a516696367f87df3f597d546206
Merge topic 'clean_coprocessing_python' into next

0df8c7d Setup default sessions during initialization.
10b2d31 Removed vtkCPPythonProcessor.
42c7dbb Clean up Python CoProcessing script logic.