* The Qt behaviour is that if you call setMinimumSize on a widget, then
the minimumSizeHint is IGNORED. So it is impossible to say "use this
minimum size, unless the widget wants a higher minimum size".
* So instead we do this ourselves in RDLabel. Sigh.
* This prevents a feedback loop where the label resizes wider to make
room for the margins, then the margins get bigger to keep the image
centred/scaled properly, etc.