QQuickScreen attached obj handles screenChanged and geometryChanged

sizeChanged is replaced with geometryChanged.  Given a Window, it also
needs to connect to the Window's screenChanged signal.  The result is
that if the screen is changed after the QQuickView is created, the
Screen attached object will be updated.

Change-Id: I64473dd960376b861eb50e3e5a1a296d0030e766
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>