WsServer and SessionProvider
Hi, i have the same problem as #643 (https://github.com/ratchetphp/Ratchet/issues/643)
```php
  $myMessaging = new myMessaging();
  $session =  new SessionProvider($myMessaging, new Handler\NativeFileSessionHandler());
  $wsServer = new WsServer($session);
  $httpServer = new HttpServer($wsServer);
  $server = IoServer::factory($httpServer, 8010, '0.0.0.0');
  $server->run();
```
And if i pass the `SessionProvider` directly into the `HttpServer` my websocket request never ends and _onOpen_ does not run

There is a reason why the `WsServer` does not pass the _$request_ attribute in _onOpen_?