PR#22 Notification transaction result status logic changes

This change recognises that the notifications can go through a long sequence of events before the final "success" or "fail". This is caught by lookin at the event type and assigning many of them to the transaction STATUS_PENDING status.

This is a minor release because the logic behind $notification_request->getTransactionStatus() has changed slightly, so some code may need revisiting, depending on how the notifications are handled.