OZG-2653 Fixed Auslesen der OrganisationsEinheitIds aus den Gruppen

src/main/java/de/itvsh/kop/user/UserResourceMapper.java

...ava/de/itvsh/kop/user/GroupRepresentationTestFactory.java

src/test/java/de/itvsh/kop/user/StubUserResource.java

...java/de/itvsh/kop/user/UserRepresentationTestFactory.java

src/test/java/de/itvsh/kop/user/UserResourceMapperTest.java

src/test/java/de/itvsh/kop/user/UserResourceTestFactory.java