Added Marianum Message pdf reader and backend

lib/data/message/messageProps.dart

@@ -0,0 +1,28 @@
+
+import 'package:marianum_mobile/api/mhsl/message/getMessages/getMessagesCache.dart';
+import 'package:marianum_mobile/api/mhsl/message/getMessages/getMessagesResponse.dart';
+import 'package:marianum_mobile/data/dataHolder.dart';
+
+import '../../api/apiResponse.dart';
+
+class MessageProps extends DataHolder {
+  GetMessagesResponse? _getMessagesResponse;
+  GetMessagesResponse get getMessagesResponse => _getMessagesResponse!;
+
+  @override
+  List<ApiResponse?> properties() {
+    return [_getMessagesResponse];
+  }
+
+  @override
+  void run({renew}) {
+    GetMessagesCache(
+        renew: renew,
+        onUpdate: (GetMessagesResponse data) => {
+          _getMessagesResponse = data,
+          notifyListeners(),
+        }
+    );
+  }
+
+}