SKOS extension should conform to our standard architecture (like SWRL, GEO and TIME)

[mdesalvo]

SKOS extension was originally developed with its own set of powerful DTOs, centered all around on SKOSConceptScheme. It should be redesigned to adhere to our standard architecture for extensions, like SWRL (starting from v3.9), GEO and TIME. A true extension layer not introducing or relying on own objects, just focused on OWLOntology and what matters for SKOS programming.