DEICH-6353 - 6XY$x$y$z mapping fix + test code improvements

DEICH-6353 - 6XYxy$z mapping fix + test code improvements

Mapping changes:
-600
Missing mapping for $y was added
-610
Had no $x/$y/$z mapping at all, was fixed.
-611
Had no $x/$y/$z mapping, fixed.
-630
Had no $x/$y/$z mapping, fixed.
-651
There was an inhereted codeing error, $x is used for reieshåndbok mapping, but if the value is not “reisehåndbøker” $x was mapped to PLACE. Fixed, $x is mapped til SUBJECT now. Added support for multiple occurrences of $x (as defined in LOC MARC21 specification).
$a and $z both maps to PLACE (was already done so before) - not changed.
$y mapping was missing, fixed.
-653
Has no $x/$y/$z.
-655
Here there is an exception, $z is mapped to Work/NATIONALITY (and this is correct this way). Otherwise added missing $x/$y mapping.

Added required tests to cover all these new cases.

Removed disabled test case test6XXxSubjects - those scenarios were covered now.

Test utility improvements:
-Renamed assertDeichModelContainsTriple to assertDeichModelContainsExactlyOneTriple, name was misleading.
Added     public static void assertDeichModelContainsSubjectPrefLabels(Model deichModel, Ontology forOntology, String ...prefLabels) replacing assertDeichModelContainsSubjectsWithPrefLabels, assertDeichModelContainsSubjectWithPrefLabel, assertDeichModelContainsSubjectPlaceWithPrefLabel

DEICH-6353 - Removed unused mapping and invalid test cases.

DEICH-6353 Mapping changes 082-083 - classification

Closes DEICH-6353