Remove blank nodes from the ontology

[mconlon17]

The ontology generates blank nodes in RDF serializations as a result of classes defined in terms of restrictions on other classes.

The RDF serializations are used in various contexts and do not constitute "5 star" linked data, nor are they consistent with Linked Data Platform specifications.

Blank nodes are also inaccessible to SPARQL queries, and confusing to those new to the Semantic Web.

Rewriting ontological assertions that generate blank nodes in serializations should have no effect on running VIVO applications, but will improve the reuse of the ontology as RDF via SPARQL and the web.