Add Subcategory / Subproperty query tests

Relates to #460
 
Skipping `SPARQLStore` because:
- Subproperty queries of type ` rdfs:subPropertyOf` are not supported by the `SPARQLStore`
- Subcategory queries of type ` rdfs:subClassOf` are not supported by the `SPARQLStore`

Skipping `Postgres` due to:
- Issue #462