fix missing trnaslation for new strings in settings dialog (bug #63404) * gui-preferences-sd.h: move new string constants to here * gui-settings.h: move new string constatns from here but leave the constants that are required in several different widgets * settings-dialog.cc (settings_dialog): use tr () for new strings here, too; (read_workspace_colors): dito; (read_terminal_colors): dito; (read_varedit_colors): dito;