Layer editor improvements3

• start layer editor in full edit mode to avoid confusion for new users
• improve in-place material editor

GUI/Models/MaterialModel.h

@@ -26,7 +26,7 @@ public:
     explicit MaterialModel(QObject* parent = nullptr);
     ~MaterialModel();
 
-    MaterialModel* createCopy(SessionItem* parent = nullptr);
+    MaterialModel* createCopy(SessionItem* parent = nullptr) override;
 
     MaterialItem* addRefractiveMaterial(const QString& name, double delta, double beta);
     MaterialItem* addSLDMaterial(const QString& name, double sld, double abs_term);