There are two unnecessary Layer warnings:
1. A 'might break' warning when deleting an object nested in a layer.
2. An 'out of scope' warning for objects also nested in f.e. a Std_Part.
To avoid them the Group property type was changed to `App::PropertyLinkListHidden`.
Discussion: #13657.
This PR adds the ShapeAppearance view property to Draft Layers.
The DefaultShapeColor is used for the DiffuseColor of the ShapeAppearance material. Other material properties are not based on the preferences when a layer is created.
The old ShapeColor and Transparency properties remain (ShapeColor as a hidden property) and are kept in synch with the ShapeAppearance. This is consistent with how ShapeAppearance is implemented in Core.
The gui_layers.py and make_layer.py files do not have to be changed. They manipulate the vobj via the mentioned old properties.
Since Py3.11 the methods names __setstate__ and __getstate__ conflict with the method names added to the object class.
Thus rename them to 'loads' and 'dumps'
Move `make_layer` to `draftmake`; `Layer` and `LayerContainer`
to `draftobjects`; `ViewProviderLayer` and `ViewProviderLayerContainer`
to `draftviewproviders`.
The make function and the classes are imported in `Draft.py`
to support the usage of the older `VisGroup`.
