[Feature Request] RO-Crate export - split ontology term accession

[floWetzels]

The RO-Crate export writes the content of termAccession in an OntologyAnnotation into the termCode property of the schema type DefinedTerm. In ISA, the termAccession is usually the full url to the term. However, as the name suggests, termCode is intended to only contain the term code (last part of the url). @JonasLukasczyk, @HLWeil and I suggest to create two schema properties from a termAccession: url (full link) and termCode (only the actual code). The logic for computing all those parts should already be available in ARCtrl.