Remove the need for the C++ PythonAlgorithm class.

This can now all be done with a templated adapter that can be resused
for exporting other Algorithm types that are to be overridden in Python.
The PythonAlgorithm name in Python is now simply an alias for Algorithm.
Refs #5157
First cut at exporting DataProcessor algorithm and basic test.

Refs #5157
Export DataProcessor algorithm to Python

It is exported so that classes in Python can inherit from it.
Refs #5157
Merge branch 'feature/5157_dataprocessor_in_python' into develop