Add a signal/virtual protected that is emitted/called when a state in the state machine is entered

Add a signal/virtual protected that is emitted/called when a state in the state machine is entered. Currently it can be done by reimplementing onEntry() or by connecting a slot to the entered signal for each QState. By adding a means at the QStateMachine level then it would be possible to call configuration() or it can be passed to do everything inside at the state machine level.