OVT-8189: Added test for levels with relation.
OVT-8189: Removed the problem with duplicate levelswith-relation when codes has a relation to self.
OVT-8189: Fixing previous mistakes.
Merge branch 'develop' of https://github.com/Opetushallitus/koodisto into develop

Conflicts:
	koodisto-service/src/test/resources/test-data.xml