Added Marianum Message pdf reader and backend

lib/api/mhsl/message/getMessages/getMessages.dart

@@ -0,0 +1,18 @@
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+import 'package:marianum_mobile/api/mhsl/message/getMessages/getMessagesResponse.dart';
+import 'package:marianum_mobile/api/mhsl/message/messageApi.dart';
+
+class GetMessages extends MessageApi<GetMessagesResponse> {
+
+  @override
+  GetMessagesResponse assemble(String raw) {
+    return GetMessagesResponse.fromJson(jsonDecode(raw));
+  }
+
+  @override
+  Future<http.Response> request(Uri uri) {
+    return http.get(uri);
+  }
+}