Checks the availability of an existing instance of the Ontology
with the given URL in the GATE's CreoleRegister. If found, returns
the first available one (doesn't guranttee in which order). If not
found, attempts to create one using OWLIM implementation with
RDF/XML as ontology type and if successful returns the newly
created instance of the ontology.
This method by using the default name space and the provided
ontology resource name, creates a new instance of URI. If
isAnonymousResource is set to true, an anonymous URI only using the
resource name is created.