DoubleSlider manipulation from preview scene

src/slic3r/GUI/GUI_Preview.hpp

@@ -122,6 +122,7 @@ public:
     void refresh_print();
 
     void msw_rescale();
+    void move_double_slider(wxKeyEvent& evt);
 
 private:
     bool init(wxWindow* parent, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar, Model* model);