Draft: split Fillet code into various modules

The original code was in `DraftFillet.py` which is split
into a different modules like the rest of the workbench.

The object code is in `draftobjects`, the viewprovider
is in `draftviewproviders`, and the function to create it
is in `draftmake`.

src/Mod/Draft/draftobjects/fillet.py

@@ -0,0 +1,123 @@
+# ***************************************************************************
+# *   Copyright (c) 2020 Eliud Cabrera Castillo <e.cabrera-castillo@tum.de> *
+# *                                                                         *
+# *   This program is free software; you can redistribute it and/or modify  *
+# *   it under the terms of the GNU Lesser General Public License (LGPL)    *
+# *   as published by the Free Software Foundation; either version 2 of     *
+# *   the License, or (at your option) any later version.                   *
+# *   for detail see the LICENCE text file.                                 *
+# *                                                                         *
+# *   This program is distributed in the hope that it will be useful,       *
+# *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+# *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+# *   GNU Library General Public License for more details.                  *
+# *                                                                         *
+# *   You should have received a copy of the GNU Library General Public     *
+# *   License along with this program; if not, write to the Free Software   *
+# *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  *
+# *   USA                                                                   *
+# *                                                                         *
+# ***************************************************************************
+"""Provides the object code for the Fillet object."""
+## @package fillet
+# \ingroup DRAFT
+# \brief Provides the object code for the Fillet object.
+
+from PySide.QtCore import QT_TRANSLATE_NOOP
+
+import FreeCAD as App
+import draftobjects.base as base
+from draftutils.messages import _msg
+
+
+class Fillet(base.DraftObject):
+    """Proxy class for the Fillet object."""
+
+    def __init__(self, obj):
+        super(Fillet, self).__init__(obj, "Fillet")
+        self._set_properties(obj)
+
+    def _set_properties(self, obj):
+        """Set the properties of objects if they don't exist."""
+        if not hasattr(obj, "Start"):
+            _tip = "The start point of this line."
+            obj.addProperty("App::PropertyVectorDistance",
+                            "Start",
+                            "Draft",
+                            QT_TRANSLATE_NOOP("App::Property", _tip))
+            obj.Start = App.Vector(0, 0, 0)
+
+        if not hasattr(obj, "End"):
+            _tip = "The end point of this line."
+            obj.addProperty("App::PropertyVectorDistance",
+                            "End",
+                            "Draft",
+                            QT_TRANSLATE_NOOP("App::Property", _tip))
+            obj.End = App.Vector(0, 0, 0)
+
+        if not hasattr(obj, "Length"):
+            _tip = "The length of this line."
+            obj.addProperty("App::PropertyLength",
+                            "Length",
+                            "Draft",
+                            QT_TRANSLATE_NOOP("App::Property", _tip))
+            obj.Length = 0
+
+        if not hasattr(obj, "FilletRadius"):
+            _tip = "Radius to use to fillet the corner."
+            obj.addProperty("App::PropertyLength",
+                            "FilletRadius",
+                            "Draft",
+                            QT_TRANSLATE_NOOP("App::Property", _tip))
+            obj.FilletRadius = 0
+
+        # TODO: these two properties should link two straight lines
+        # or edges so we can use them to build a fillet from them.
+        # if not hasattr(obj, "Edge1"):
+        #    _tip = "First line used as reference."
+        #    obj.addProperty("App::PropertyLinkGlobal",
+        #                    "Edge1",
+        #                    "Draft",
+        #                    QT_TRANSLATE_NOOP("App::Property", _tip))
+
+        # if not hasattr(obj, "Edge2"):
+        #    _tip = "Second line used as reference."
+        #    obj.addProperty("App::PropertyLinkGlobal",
+        #                    "Edge2",
+        #                    "Draft",
+        #                    QT_TRANSLATE_NOOP("App::Property", _tip))
+
+        # Read only, change to 0 to make it editable.
+        # The Fillet Radius should be made editable
+        # when we are able to recalculate the arc of the fillet.
+        obj.setEditorMode("Start", 1)
+        obj.setEditorMode("End", 1)
+        obj.setEditorMode("Length", 1)
+        obj.setEditorMode("FilletRadius", 1)
+        # obj.setEditorMode("Edge1", 1)
+        # obj.setEditorMode("Edge2", 1)
+
+    def execute(self, obj):
+        """Run when the object is created or recomputed."""
+        if hasattr(obj, "Length"):
+            obj.Length = obj.Shape.Length
+        if hasattr(obj, "Start"):
+            obj.Start = obj.Shape.Vertexes[0].Point
+        if hasattr(obj, "End"):
+            obj.End = obj.Shape.Vertexes[-1].Point
+
+    def _update_radius(self, obj, radius):
+        if (hasattr(obj, "Line1") and hasattr(obj, "Line2")
+                and obj.Line1 and obj.Line2):
+            _msg("Recalculate the radius with objects.")
+
+        _msg("Update radius currently not implemented: r={}".format(radius))
+
+    def onChanged(self, obj, prop):
+        """Change the radius of fillet. NOT IMPLEMENTED.
+
+        This should automatically recalculate the new fillet
+        based on the new value of `FilletRadius`.
+        """
+        if prop in "FilletRadius":
+            self._update_radius(obj, obj.FilletRadius)