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/m-editor/file-editor.cc	Wed Dec 11 16:37:28 2019 -0800
+++ b/libgui/src/m-editor/file-editor.cc	Thu Dec 12 06:45:57 2019 +0100
@@ -230,7 +230,8 @@
   {
     resource_manager& rmgr = m_octave_qobj.get_resource_manager ();
     gui_settings *settings = rmgr.get_settings ();
-    if (settings->value ("useCustomFileEditor",false).toBool ())
+    if (settings->value (global_use_custom_editor.key,
+                         global_use_custom_editor.def).toBool ())
       return;  // do not open an empty script in the external editor
 
     bool real_visible;
@@ -2534,7 +2535,8 @@
     resource_manager& rmgr = m_octave_qobj.get_resource_manager ();
     gui_settings *settings = rmgr.get_settings ();
 
-    if (settings->value ("useCustomFileEditor",false).toBool ())
+    if (settings->value (global_use_custom_editor.key,
+                         global_use_custom_editor.def).toBool ())
       {
         // use the external editor interface for handling the call
         emit request_open_file_external (file_name, line);