Update to Datacite 4.6

[Zack-83]

The DataCite Consortium has recently deprecated all older schema versions, including v3.1, which this ontology reproduces.

Maybe it is time to create a new version of the ontology? I volunteer to help.

Best regards

Giacomo Lanza (PTB, Germany)

[Zack-83]

I can see that another repository has already reproduced the DataCite schema 4.6 as a XML schema and a JSON schema, thus defining their own namespace: inveniosoftware/datacite#115

I did not check how far their namespace definition is compatible with the SPAR model, but if there is any interest on your side we can work on it!