add IWantToKnowWhenIFail.OnFinalFailure

- subscribers can implement this interface to know when a message has failed and won't be retried
throw ex in LoserMsgSubscriber.OnFinalFailure to validate acceptance criteria
Merge pull request #62 from daptiv/68016-IWantToKnowWhenIFail

68016 i want to know when i fail