Remove PythonAPI directory and most references

The link to the system installed/3rd party version of boost python
is now restored.

This required an additional helper function: isNone. boost python
only introduced object::is_none in version 1.43 so the helper
uses it if it is present but falls back to checking manually if not.

Refs #7607
Merge branch 'feature/7607_remove_v1_python_api' into develop