subClassOf propery is not handled correctly.

[manfredhod]

Describe the bug
When loading the Clinical Trials Ontology none of the SubClassOf properties are serialized or rendered. However testing with the SPARQL Playground the default SPARQL query is able to detect the triples. This can be seen in the picture below:

To Reproduce
Load Clinical Trials Ontology into VOWL-R.

Expected behavior
We should be able to serialize these SubClassOf properties correctly and visualize them.

[khmikkelsen]

From line 943-950:

<!-- http://www.w3.org/2000/01/rdf-schema#subClassOf -->

<owl:ObjectProperty rdf:about="http://www.w3.org/2000/01/rdf-schema#subClassOf">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#TransitiveProperty"/>
    <obo:IAO_0000412 rdf:resource="http://purl.obolibrary.org/obo/gaz.owl"/>
    <obo:IAO_0000412 rdf:resource="http://purl.obolibrary.org/obo/opmi.owl"/>
</owl:ObjectProperty>

It's declaring rdf sub class of to be a transitive property.. And because it's schema doesnt fit to documentbase, sub class is inserted as an ExternalProperty.

[TheRealMorgenfrue]

That should be fixable by checking IRIs against resolvable_iris