Use Websocket to update number of unread notifications

lib/models/count_unread_notifications.dart

@@ -3,8 +3,8 @@
 /// @author Pierre Hubert
 
 class CountUnreadNotifications {
-  final int notifications;
-  final int conversations;
+  int notifications;
+  int conversations;
 
   CountUnreadNotifications({
     this.notifications,

lib/models/ws_message.dart

@@ -0,0 +1,25 @@
+import 'package:flutter/widgets.dart';
+
+/// WebSocket message
+///
+/// @author Pierre Hubert
+
+class WsMessage {
+  final String id;
+  final String title;
+  final dynamic data;
+
+  const WsMessage({
+    @required this.id,
+    @required this.title,
+    @required this.data,
+  })  : assert(id != null),
+        assert(title != null);
+
+  /// Construct a message from a JSON document (messages coming from the server)
+  static WsMessage fromJSON(final Map<dynamic, dynamic> m) {
+    return WsMessage(id: m["id"], title: m["title"], data: m["data"]);
+  }
+
+  bool get hasId => this.id != null && this.id.isNotEmpty;
+}