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`.
Since we know how the old class looks like,
we can write code to save the value of the older properties,
and then remove them.
Then we can assign the new class, which will create new properties,
and then we can assign the old values to these.
This can be done for both the proxy object and
for the viewprovider.
Identify the previous object as `DraftFillet.Fillet`
and then use the new proxy class `draftobjects.fillet.Fillet`
and new viewprovider `view_fillet.ViewProviderFillet` on it.
Remove the make function that creates the old object,
its corresponding Gui Command, and the old `DraftFillet.Fillet`
proxy class, which now is a redirection to the new `Fillet`
class defined in `draftobjects.fillet`.
Also change the unit test, and the `draft_test_object` script
to run `Draft.make_fillet`.
