implement tests for RdfConverter
	- writeSubclassOf statements
	- writeSimpleStatements
	- task taxonomy test
some changes for the ValueRdfConverterTests
Merge branch 'master' of
https://github.com/Wikidata/Wikidata-Toolkit.git into
rdf-serializer_tests

Conflicts:
	wdtk-rdf/src/main/resources/GlobeCoordinatesValue.rdf
	wdtk-rdf/src/main/resources/QuantityValue.rdf
	wdtk-rdf/src/main/resources/TimeValue.rdf
make test objects more consistent
Merge pull request #76 from Wikidata/rdf-serializer_tests

Rdf serializer tests