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
Uses new material system for appearance
Each feature object now has a property called ShapeMaterial that
describes its physical properties. If it has a shape, it has a
material.
The ShapeColor attribute is replaced by a ShapeAppearance attribute.
This is a material list that describes all appearance properties, not
just diffuse color. As a list in can be used for all elements of a
shape, such as edges and faces.
A new widget is provided to allow the user to select materials in a
consistent fashion. It can also launch the material editor with its
more advanced capabilities.
Replace the hard-coded XPM icon in `InitGui.py` for the workbench
with an SVG file, which at this time is identical to the `Surface` icon.
Change `CMakeLists.txt` to properly install this new icon.
Rename all icons, so that all have the `Surface_` prefix.
Use the new icon names in the viewproviders and task panels.
