Deletion of instances and volumes from 3D scene

src/slic3r/GUI/GLCanvas3DManager.hpp

@@ -140,6 +140,8 @@ public:
 
     void render(wxGLCanvas* canvas) const;
 
+    void delete_selected(wxGLCanvas* canvas);
+
     std::vector<double> get_current_print_zs(wxGLCanvas* canvas, bool active_only) const;
     void set_toolpaths_range(wxGLCanvas* canvas, double low, double high);