Add a new QMarginsF class to complement QMargins in the style of
QSize/QSizeF and QRect/QRectF.
[ChangeLog][QtCore] Added class QMarginsF to support handling margins
with floating-point values.
Change-Id: Iaaa95ec85f5d126d9d864fc4b607241a8c8a8f3a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>