Add setting to enable flipping direction of all train types in depot

src/settings_gui.cpp

@@ -1714,6 +1714,7 @@ static SettingsContainer &GetSettingsTree()
 			vehicles->Add(new SettingEntry("order.serviceathelipad"));
 			vehicles->Add(new SettingEntry("vehicle.adjacent_crossings"));
 			vehicles->Add(new SettingEntry("vehicle.safer_crossings"));
+			vehicles->Add(new SettingEntry("vehicle.flip_direction_all_trains"));
 		}
 
 		SettingsPage *limitations = main->Add(new SettingsPage(STR_CONFIG_SETTING_LIMITATIONS));