change WebAPI datatypes to datatype IRIs in KNOWN_PROPERTY_TYPES
Merge branch 'rdf-serializer' of
https://github.com/Wikidata/Wikidata-Toolkit.git into rdf-serializer

Conflicts:
	wdtk-rdf/src/main/java/org/wikidata/wdtk/rdf/ValueRdfConverter.java