Set Python DeprecationWarnings to default. Refs #6639

In 2.7 they are ignored by default, which is not that useful.
Fix doxygen errors in Python Axis.cpp. Refs #6639
Add deprecated functions to new API to aid in transition. Refs #6639
Merge branch 'feature/6639_deprecated_python_cmds' into develop.

Refs #6639

Conflicts:
	Code/Mantid/Framework/PythonInterface/mantid/api/src/Exports/Axis.cpp