Fix ontology rdfs:subClassOf to use JSON-LD @id nodes (closes #685)
Fixes #685 (closed) for the v1.0.0 / WIP ontology line: eight rdfs:subClassOf values were JSON-LD string literals and are now {"@id": ...} node references. No intentional model change. Frozen 0.7.0 published vocabulary remains as released. Closes #685 (closed).