Material: Material Preferences

Updates the material preferences including selecting a default material

Preferences adds some options for what gets displayed in the Materials editor.
The option to use the legacy editor is removed in favour of the new
editor.

A new preference page has been added that allows the user to select a
default material. This will then be assigned to any newly created object. In
support of this, a new widget PrefsMaterialTreeWidget has been added as an
extension of the MaterialTreeWidget to automatically save and restore the
selected material.

src/Mod/Material/App/MaterialManager.h

@@ -55,6 +55,7 @@ public:
     ~MaterialManager() override = default;
 
     static void cleanup();
+    static void refresh();
     static std::shared_ptr<Material> defaultMaterial();
     static QString defaultMaterialUUID();