BibClassify: PEP8 and PEP257 fix
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 <8d55e006a1b29770f275a5c59a7341f17f8e69d5@cern.ch>
Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

tiborsimko/invenio,inveniosoftware/invenio,tiborsimko/invenio,inveniosoftware/invenio