Delaying notifications possible in multiple ways

[rvdsteege]

Notifications can be delayed until the payment has been completed successfully. However, this can currently be done in multiple ways:

1. via the Event setting of a notification
2. via the payment feed settings.

The event also makes it possible to send notifications for other events, such as a failed payment. I'd suggest removing the original functionality to delay notifications through the payment feed settings in favour of the notification event.