Fixed copying of some object's attributes into the clipboard

(layer height profile, layer height table etc)
Added public Plater::schedule_background_process()

src/slic3r/GUI/Plater.hpp

@@ -162,6 +162,7 @@ public:
     void reslice();
     void reslice_SLA_supports(const ModelObject &object);
     void changed_object(int obj_idx);
+    void schedule_background_process();
     void fix_through_netfabb(const int obj_idx, const int vol_idx = -1);
     void send_gcode();