replace literal strings by symbolic constants for global preferences * default-qt-settings.in: removed default values from the global section * dialog.cc: include gui-preferences-global.h; (FileDialog::FileDialog): replaced literals by symbolic constants * external-editor-interface.cc: include gui-preferences-global.h; (external_editor): replaced literals by symbolic constants * find-files-dialog.cc: include gui-preferences-global.h; (browse_folders): replaced literals by symbolic constants * gui-preferences-global.h: added symbolic constants for key names and default values for preferences in the global section of the settings file * file-editor-tab.cc (save_file_as): replaced literals by symbolic constants * file-editor.cc (empty_script, call_custom_editor): replaced literals by symbolic constants * main-window.cc (confirm_shutdown, handle_save_workspace_request, handle_load_workspace_request, notice_settings, browse_for_directory, request_open_file, request_new_function, handle_octave_ready): replaced literals by symbolic constants * resource-manager.cc (config_translators, update_network_settings): replaced literals by symbolic constants * settings-dialog.cc (settings_dialog, write_changed_settings): replaced literals by symbolic constants * shortcut-manager.cc: include gui-preferences-global.h; (import_export): replaced literals by symbolic constants

--- a/libgui/src/external-editor-interface.cc	Wed Dec 11 16:37:28 2019 -0800
+++ b/libgui/src/external-editor-interface.cc	Thu Dec 12 06:45:57 2019 +0100
@@ -29,6 +29,7 @@
 
 #include "external-editor-interface.h"
 #include "gui-settings.h"
+#include "gui-preferences-global.h"
 #include "octave-qobject.h"
 
 namespace octave
@@ -100,7 +101,8 @@
   {
     resource_manager& rmgr = m_octave_qobj.get_resource_manager ();
     gui_settings *settings = rmgr.get_settings ();
-    QString editor = settings->value ("customFileEditor").toString ();
+    QString editor = settings->value (global_custom_editor.key,
+                                      global_custom_editor.def).toString ();
 
     // check the settings (avoid an empty string)
     if (editor.trimmed ().isEmpty ())