_object_value and _object_value_list return BNode identifiers about ckanext-dcat

[amercader]

I think these cases should be handled in the parser methods, and I agree that it's useless to store the BNode value.

Perhaps if the object in in _object_value (or one of the items in _object_value_list it's a BNode then we inspect that node and extract whatever makes more sense, a Literal if it's there, or the value of skos:prefLabel if it's a node of type skos:concept. That should hopefully cover the theme case.

BTW this particular serialization for provenance is not a valid JSON-LD, @label is not a valid keyword. I'm by no means a JSON-LD expert but I think @value should be used instead (otherwise rdflib can not extract anything from that node):

			"dct:provenance": {
				"@type": "dct:ProvenanceStatement",
			        "@value": "Something actually useful"

			},