Use Q_DECL_OVERRIDE where applicable.

Task-number: QTBUG-41130
Change-Id: I4951e2cc27d5652fd9802216511bbc3a4cdeb186
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
De-inline QAxAggregated::widget().

The QWidget-class definition might not be present when
using QAxAggregate with QAxWindow.

Task-number: QTBUG-41130
Change-Id: Ib8f2097ebdc6af13e3f1e1b51bfcd23512564c0b
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>