Graph# to GraphX unfinished migration attempt.
Graph features partially restored. (...)

- Active bug: Graph is not displayed when there is a single vertex.
- Restored unselect on background click.
- Restored drag.
Added edge tags, restored layout change feature.
Removed Main window VM strict dependency to UI Window. Fixes lab tests.
Added default state, loaded when application satrts. (...)

- Added default tree layout.
Lab: Model safeguard against generalization loops
Lab/Service properties: Setting Generalization can now fail with a message. (...)

- Added partially-active design-time model.
Merge branch 'feature/lab-migrate-from-graphsharp-to-graphx' into develop
Adapted Lab to new Engine. (...)

- Saving and Loading are temporarily disabled until the ConfigurationManager Serializer is back up. An incomplete loading is to be expected before that.
- Removed DesignModel.
- ConfigurationEditor XAML: As interfaces aren't supported in DataTemplate DataTypes, we are now using them directly nested to the ItemsControl.
- Live infos: Most functions are not implemented yet.