Access rights code list

[andrea-perego]

The usage note for dct:accessRights says in §4.12.3:

This property refers to information that indicates whether the Dataset is open data, has access restrictions or is not public. A controlled vocabulary with three members (:public, :restricted, :non-public) will be created and maintained by the Publications Office of the EU.

A code list with those values have been actually published by the OP, so the usage note should be updated accordingly.

See also SEMICeu/DCAT-AP#159