Refactored the data structure storing the metric data

...ss/tooling/ext/quality/ui/ModelQualityExtractionMenu.java

...s/tooling/ext/quality/ui/view/fx/MetricsFXController.java

org.fortiss.tooling.ext.quality/META-INF/MANIFEST.MF

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

...ss/tooling/ext/quality/HierarchicElementSizeProvider.java

...rg/fortiss/tooling/ext/quality/IModelQualityProvider.java

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

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

...g/fortiss/tooling/ext/quality/data/MetricDataManager.java

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

...iss/tooling/ext/quality/service/IModelQualityService.java

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