BibClassify: PEP8 and PEP257 fix

• Improves PEP8 and PEP257 across ontology_reader.

• NOTE Removes any rdflib checks which are no longer needed as this library is (1) mandatory and (2) mandatory at a high version.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>