QNX: add nativeResourceForScreen

Implemented nativeResourceForScreen api to return QObject* which can be used to connect  foreignWindowCreated, foreignWindowClosed signal in QQnxScreen.
Usecase is to connect signal in custom QML component as below
	QObject * obs = interface->nativeResourceForScreen("QObject*", screen);
	connect(obs, SIGNAL(foreignWindowCreated(void*)), d, SLOT(newForeignWindowCreated(void*)));

Change-Id: I512c3b6d188a2e90ef7b8e89c413ca420a29dd9b
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>