Implemented another behavior of the "Slice Now" / "Export/Send G-code" buttons (SPE-831)

src/slic3r/GUI/BackgroundSlicingProcess.hpp

@@ -123,6 +123,9 @@ public:
     // This "finished" flag does not account for the final export of the output file (.gcode or zipped PNGs),
     // and it does not account for the OctoPrint scheduling.
     bool    finished() const { return m_print->finished(); }
+    
+    // set status line
+    void    set_status(const std::string & status_str) const { m_print->set_status(100, status_str); }
 
 private:
 	void 	thread_proc();