[Unit Tests] RelationshipsMatrix should return unmodifiable Map types
[Unit Tests] TreeModelViewerDragDropHandler refactor and Unit Test overkill
[Unit Tests] MRUMenuManager refactor and Unit Tests
[Unit Tests] StringUtils: add compareVersionNumbers() method and tests
[Unit Tests] CheckForNewVersionAction refactor and Unit Tests
[Unit Tests] ModelCompatibility uses StringUtils.compareVersionNumbers()
[Unit Tests] Some corrections to tests and tested objects
[Unit Tests] Add DiagramModelUtils and Nested Relations tests

* Also upgrade ArchimateTestModel for more utils
[Unit Tests] Add DeleteCommandHandlerTests
Merge branch 'unit-tests'