cleanups
SubGraph: correct handling of ChangeEdge
Graph.DoDataChange: use ist in ThingGraphExtensions and VisualThingSceneViz
TestFactories: wording and moved
SceneFacadeTest: introduced a Wrapper for easier handling | GraphSceneMeshTest: refactored to use TestWraper and  tests extended to multiple Displays
GraphSceneLayout: AdjustSize introduced
Aligner:.AffectedEdges: extend to give back edges as leaf or root
GraphSceneMesh: moved and minor changes
GraphSceneFolding: use more keys to collapse/expand
TextEditAction: catch error if value not convertible
DigidocViewer: Mesh.AddDisplay(pagesDisplay)