Saving the resulting ontology in different syntaxes

[pedropaulofb]

Currently, OntCatOWL only saves the output ontology in ttl, but saving the resulting ontology in a different syntax using RDFLib is really simple.

We could implement this feature in OntCatOWL to possibility simplify things to users. They could simply add an argument informing which is the desired output syntax.

Reference: https://rdflib.readthedocs.io/en/stable/intro_to_parsing.html#saving-rdf