* remove unused else
* Enable reloading / re-selection of libraries
* Reload the libraries when exiting the editor
* Clear the model to prevent duplicate entries
* add missing docstring to reduce linting warnings
* Maintain any previous library selection when editing
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.
