reworked page layout inheritence

frontend/lib/structs/landmark.dart

@@ -70,10 +70,10 @@ final class Landmark extends LinkedListEntry<Landmark>{
       final websiteURL = json['website_url'] as String?;
       final imageURL = json['image_url'] as String?;
       final description = json['description'] as String?;
-      var duration = Duration(minutes: json['duration'] ?? 0) as Duration?;
-      final visited = json['visited'] ?? false as bool;
+      var duration = Duration(minutes: json['duration']);
+      final visited = json['visited'] ?? false;
       var tripTime = Duration(minutes: json['time_to_reach_next'] ?? 0) as Duration?;
-      
+
       return Landmark(
         uuid: uuid,
         name: name,

frontend/lib/structs/trip.dart

@@ -29,6 +29,18 @@ class Trip with ChangeNotifier {
     }
   }
 
+  Future<int> landmarkPosition (Landmark landmark) async {
+    int i = 0;
+    for (Landmark l in landmarks) {
+      if (l.uuid == landmark.uuid) {
+        return i;
+      } else if (l.type != typeStart && l.type != typeFinish) {
+      i++;
+      }
+    }
+    return -1;
+  }
+
 
   Trip({
     this.uuid = 'pending',