refactored the visualizer. The cluster tree is now has a proper layout. I had to remove the data label, because it doesn't appear to work. All json in visualizationPlugin is now serialized in POJO's
Merge branch 'development_thijl' into new-data-objects
Merge branch 'new-data-objects' of https://github.com/flexiblepower/powermatcher into new-data-objects