BibClassify: error handling and PEP8
- Adds a new exception type TaxonomyError when there is a problem reading the ontology passed to legacy BibClassify.
- Performs some PEP8 fixes across ontology_reader.py and engine.py.
Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
Reviewed-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>