implemented a backend-independent emergency notice system

lib/view/pages/settings/data/default_settings.dart

@@ -75,6 +75,7 @@ class DefaultSettings {
       showPerformanceOverlay: false,
       marianumConnectEndpoint: MarianumConnectEndpoint.live,
       marianumConnectCustomUrl: '',
+      emergencyNoticeUrl: '',
     ),
     hapticSettings: HapticSettings(level: HapticLevel.full),
   );