Set parent of internal server objects

After moving the websocket server into another thread
current code doesn't work because then the QTcpServer/QSslServer
objects reside in a different thread:
"QWarning: QObject: Cannot create children for a parent that is in a different thread."

QObject::moveToThread(QThread*) also moves QObjects's children, therefore the
internal server objects need to be children of QWebSocketServer.

Change-Id: Ic7e8a564cd87400a4ab7258e3799157ed359c098
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>