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/MessageUserPosition.ts

@@ -0,0 +1,24 @@
+import {Message} from "./Message";
+
+export class MessageUserPosition extends Message{
+    positionXUser: string;
+    positionYUser: string;
+
+    constructor(message: string) {
+        super(message);
+        let data = JSON.parse(message);
+        this.positionXUser = data.positionXUser;
+        this.positionYUser = data.positionYUser;
+    }
+
+    toString() {
+        return JSON.stringify(
+            Object.assign(
+                super.toJson(),
+                {
+                    positionXUser: this.positionXUser,
+                    positionYUser: this.positionYUser
+                })
+        );
+    }
+}