Map upper-level concepts to ML-Schema

[epatters]

ML-Schema is an upper ontology for machine learning workflows, inspired by OpenML's data model and created by @joaquinvanschoren and others.

We should map the upper-level concepts in the DSO, like model and data, to concepts in ML-Schema. Actually, the overlap is currently not too big but it may grow over time.

This mapping should be implemented by

• external resources in the native format, as we do for Wikidata concepts
• suitable OWL statements in the RDF/OWL export