Draft: migrate Layer object and function to the new structure

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`.

src/Mod/Draft/CMakeLists.txt

@@ -117,6 +117,7 @@ SET(Draft_make_functions
     draftmake/make_facebinder.py
     draftmake/make_fillet.py
     draftmake/make_label.py
+    draftmake/make_layer.py
     draftmake/make_line.py
     draftmake/make_orthoarray.py
     draftmake/make_patharray.py
@@ -150,6 +151,7 @@ SET(Draft_objects
     draftobjects/fillet.py
     draftobjects/draftlink.py
     draftobjects/label.py
+    draftobjects/layer.py
     draftobjects/dimension.py
     draftobjects/patharray.py
     draftobjects/point.py
@@ -179,6 +181,7 @@ SET(Draft_view_providers
     draftviewproviders/view_fillet.py
     draftviewproviders/view_draftlink.py
     draftviewproviders/view_label.py
+    draftviewproviders/view_layer.py
     draftviewproviders/view_dimension.py
     draftviewproviders/view_point.py
     draftviewproviders/view_rectangle.py

src/Mod/Draft/Draft.py

@@ -368,10 +368,15 @@
 if App.GuiUp:
     from draftviewproviders.view_fillet import ViewProviderFillet
 
-# Layers
-from DraftLayer import Layer as _VisGroup
-from DraftLayer import ViewProviderLayer as _ViewProviderVisGroup
-from DraftLayer import makeLayer
+from draftobjects.layer import (Layer,
+                                _VisGroup)
+
+from draftmake.make_layer import (make_layer,
+                                  makeLayer)
+
+if App.GuiUp:
+    from draftviewproviders.view_layer import (ViewProviderLayer,
+                                               _ViewProviderVisGroup)
 
 # Annotation objects
 from draftobjects.dimension import (LinearDimension,

src/Mod/Draft/DraftFillet.py

@@ -45,16 +45,18 @@
 with the 0.19 development version.
 
 Since this module is only used to migrate older objects, it is only temporary,
-and will be removed after one year of the original introduction of the tool,
-that is, in August 2020.
+and will be removed after one year, that is, in January 2021.
+
+The explanation of the migration methods is in the wiki page:
+https://wiki.freecadweb.org/Scripted_objects_migration
 """
 ## @package DraftFillet
 # \ingroup DRAFT
 # \brief Provides Fillet class for objects created with a prototype version.
 #
 # This module is only required to migrate old objects created
 # from August 2019 to February 2020. It will be removed definitely
-# in August 2020, as the new Fillet object should be available.
+# in January 2021, as the new Fillet object should be available.
 
 import FreeCAD as App
 import draftobjects.fillet