save and restore last geometry of load path dialog * gui-preferences.h: define key and emtpy default for path dialog geometry * main-window.cc (prepare_to_exit): save settings of path dialog if the related pointer is valid * set-path-dialog.cc: include gui-preferences.h with new preference key; (set_path_dialog): restore last geometry from preferences file; (save_settings): new method for saving geoemtry and possibly other preferences when the dialog is closed or when octave is about to quit; (closeEvent) reimplement close event for saving settings before closing * set-path-dialog.h: new method save_settings, new protected close event

--- a/libgui/src/main-window.cc	Sun Aug 04 08:52:27 2019 +0200
+++ b/libgui/src/main-window.cc	Sun Aug 04 20:53:17 2019 +0200
@@ -928,6 +928,9 @@
     if (m_find_files_dlg)
       m_find_files_dlg->save_settings ();
 
+    if (m_set_path_dlg)
+      m_set_path_dlg->save_settings ();
+
     write_settings ();
   }