If the submission failed, we probably want to try again next time around.
* src/server/service/RatingServiceSubmitNotify.js
(_maybeNotify): Extract logic from `#postProcessRaterData'. Only set
notification flag in absence of dapi error.
(postProcessRaterData): Use it.
* test/server/service/RatingServiceSubmitNotifyTest.js: Update tests
accordingly.
* src/server/db/MongoServerDao.js
(getDocumentField,setDocumentField): New methods.
* src/server/service/RatingServiceSubmitNotify.js
(postProcessRaterData): Only notify when notification flag is not set.
(_getNotifyState, _setNotified): New methods.
* test/server/service/RatingServiceSubmitNotifyTest.js: Modify accordingly.