AdjunctBatch raises completed notification

[donaldgray]

AdjunctBatch should publish to an SNS topic on completion of a batch. This could happen in the API or Engine. This is similar to how Batch completion notifications are currently raised.

• API will raise completed notification if all adjuncts in a batch are set to 'finished'.
• Engine will raise completed notification if the currently processed adjunct is the last adjunct to be 'finished', regardless of whether it was successful or not.