Doc: Fixed QtQuick.Window documentation

-fixed import statement in \qmlmodule and \inqmlmodule command.
-Removed extra identifier in property documentation.

Task-number: QTBUG-33360
Change-Id: I1e7ca5f418c327d42247ab4f4a11733c63d8c273
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>