Reworked sys_color_changed() functions

Fixed OSX specific bugs:
- toolbar flashing for some mainframe sizes (Retina specific)
- size of mainframe when settings layout in slNew mode

Added missed icons to the "white" folder

src/slic3r/GUI/GUI_ObjectLayers.hpp

@@ -94,6 +94,7 @@ public:
 
     void        UpdateAndShow(const bool show) override;
     void        msw_rescale();
+    void        sys_color_changed();
     void        reset_selection();
     void        set_selectable_range(const t_layer_height_range& range) { m_selectable_range = range; }