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'
The "Merge layer duplicates" Tree view context menu option for LayerContainers did not work.
Additionally:
- Using `openTransaction` and `commitTransaction` is required for the `merge_by_name` function but also for the `add_layer` function. Otherwise undo-redo does not work properly.
- Have replaced `translate("Draft", ...)` with `_tr(...)`.
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`.
