Added Marianum Message pdf reader and backend

lib/api/mhsl/message/messageApi.dart

@@ -0,0 +1,22 @@
+import 'package:http/http.dart' as http;
+import '../../apiError.dart';
+import '../../apiRequest.dart';
+
+abstract class MessageApi<T> extends ApiRequest {
+  String path = "https://mhsl.eu/marianum/marianummobile/message/messages.json";
+  http.Response? response;
+
+  Future<http.Response>? request(Uri uri);
+  T assemble(String raw);
+
+  Future<T> run() async {
+    Uri endpoint = Uri.parse(path);
+
+    http.Response? data = await request(endpoint);
+    if(data == null) {
+      throw ApiError("Request could not be dispatched!");
+    }
+
+    return assemble(data.body);
+  }
+}