Fix up listening for layout direction changes.

Change the event type to ApplicationLayoutDirectionChange. LayoutDirectionChange
is sent for QWidgets only at present, and was wrong anyway: each widget may have
a different layoutDirection, but the application instance only has one -- tied
to ApplicationLayoutDirectionChange.

Relies on I2d2ac7dc07f11be5c7e501a3575b1d0978d8ac31 from qtbase to actually function.

Task-number: QTBUG-21573
Change-Id: Ibee25927b2213ae9145d46556698f54d5129bd06
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>