Comments were corrected for constructors. GeometryFactoryBase is extracted.
Update of the StageContentView was fixed
Logic for selection of items in scene-content view are implemented.
SelectedItems collection and  SelectedSceneEntitiesChanged events were added to SceneContent
Details are shown for selected scene-entity.
Names are shown in the scene-entities list.
Names of the selected scene-entity can be changed in the detail-view.