Material: Appearance Updates 2

Improves the use of the ShapeAppearance property for the Part workbench.

    removes DiffuseColor property
        adds Python compatibility using custom attributes
        transitions DiffuseColor to ShapeAppearance on open
    Improved UI elements for setting object appearance, and appearance per face
    Lays the foundation for future texture support

src/Gui/Application.h

@@ -271,7 +271,7 @@ protected:
          std::make_pair(QT_TRANSLATE_NOOP("EditMode", "Color"),
                         QT_TRANSLATE_NOOP("EditMode",
                                           "The object will have the color of its individual faces "
-                                          "editable with the Part FaceColors command"))},
+                                          "editable with the Part FaceAppearances command"))},
     };
     int userEditMode = userEditModes.begin()->first;