Add splitMeshIntoConnectedParts to LibRenderingExt and to mesh-tool-menu.
Adapt to changes in E_MinSG/SceneManagement.
PADrend: Allow multiple independent sceneManagers for independent namespaces.

- PADrend.SceneManagement.loadScene(...) add sceneManager paramter.
- Adapt toolbar and scene load dialog.
- ...
ObjectTraits: Add NamedLocationsTrait.
MeshMenu: Adjust "split mesh" parameters.