[PyQt] Add "user" property to a widget

[Arve Knudsen]

I need to have a "user" property for a widget, so it can be fetched
via its metaObject().userProperty(). This is required since the
convention in Qt is to designate a "user" property of a widget for
editing purposes (e.g., text() for QLineEdit). Now that I've explained
my use case, how can I can define such a property in PyQt :)

Thanks,
Arve