Add io socket message to share user position.

- Add message 'user-position' to share position in a room.
 - Change JoinRoomMessage to MessageUserPosition to have all data to share position and user information
 - Fix error alias to build

back/src/Model/Websocket/Message.ts

@@ -0,0 +1,17 @@
+export class Message {
+    userId: string;
+    roomId: string;
+
+    constructor(message: string) {
+        let data = JSON.parse(message);
+        this.userId = data.userId;
+        this.roomId = data.roomId;
+    }
+
+    toJson() {
+        return {
+            userId: this.userId,
+            roomId: this.roomId,
+        }
+    }
+}