ui improvements for trips and landmarks

frontend/lib/structs/trip.dart

@@ -16,11 +16,15 @@ class Trip with ChangeNotifier {
   // could be empty as well
 
   Future<String> get cityName async {
+    List<double>? location = landmarks.firstOrNull?.location; 
     if (GeocodingPlatform.instance == null) {
-      return '${landmarks.first.location[0]}, ${landmarks.first.location[1]}';
+      return '$location';
+    } else if (location == null) {
+      return 'Unknown';
+    } else{
+      List<Placemark> placemarks = await placemarkFromCoordinates(location[0], location[1]);
+      return placemarks.first.locality ?? 'Unknown';
     }
-    List<Placemark> placemarks = await placemarkFromCoordinates(landmarks.first.location[0], landmarks.first.location[1]);
-    return placemarks.first.locality ?? 'Unknown';
   }
 
 
@@ -56,6 +60,11 @@ class Trip with ChangeNotifier {
     notifyListeners();
   }
 
+  void removeLandmark(Landmark landmark) {
+    landmarks.remove(landmark);
+    notifyListeners();
+  }
+
   factory Trip.fromPrefs(SharedPreferences prefs, String uuid) {
     String? content = prefs.getString('trip_$uuid');
     Map<String, dynamic> json = jsonDecode(content!);