[Development] Adding Q_GADGET here and there

[Alberto Mardegan]

On 16/04/2017 21:13, Olivier Goffart wrote:
> 
> Q_GADGET's overhead is basically the cost of the QMetaObject. So it's there, 
> but it's quite small.
> If there is an use for a class to be a Q_GADGET, I think it should be added.

For the record:
https://codereview.qt-project.org/#/c/191777/

Ciao,
  Alberto