Remove unused ctors and dtor, add Q_OBJECT, indent,
privatize slots, don't check for nullptr before
delete'ing a pointer, and add one override keyword.
Setting test_box (a QPointer) to nullptr is already
done by the variable's default ctor.
Change-Id: I13f06dc8104ef1c0ac08a25c960641c076f10499
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
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