configuration updater

forced update dialog
check for updates button
check address when downloading bundles

src/slic3r/GUI/GUI_App.hpp

@@ -200,6 +200,7 @@ private:
     bool            select_language();
 
     bool            config_wizard_startup();
+	void            check_updates(const bool verbose);
 
 #ifdef __WXMSW__
     void            associate_3mf_files();