cython: move code out of the header file

This routine is not performance-critical; there is no reason
why it can't live in the C file instead of the header.
A side effect is that the header include heirarchy is cleaned up.
Sketch a python GroundedSchemaNode

I can't figure out how to invoke python from opencog.
Merge pull request #150 from linas/python-game

Python grounded schema node