Cleanup and refactor of MetricTreeNode

...tooling/ext/quality/ui/view/fx/IModelQualityViewPart.java

...ling/ext/quality/ui/view/fx/ModelQualityFXController.java

...ooling/ext/quality/ui/view/fx/ModelQualityFXViewPart.java

.../org/fortiss/tooling/ext/quality/AF3QualityActivator.java

...ortiss/tooling/ext/quality/HierarchicElementProvider.java

...ing/ext/quality/data/HierarchicalMetricDataContainer.java

...ortiss/tooling/ext/quality/data/IMetricDataContainer.java

...y/src/org/fortiss/tooling/ext/quality/data/MetricKey.java

.../org/fortiss/tooling/ext/quality/data/MetricTreeNode.java

...src/org/fortiss/tooling/ext/quality/io/CSVFileWriter.java

...tiss/tooling/ext/quality/service/ModelQualityService.java