Retry notifications untill success

Follow https://git.startinblox.com/components/sib-chat/issues/99#note_26220

May need a more precise spec, see https://git.startinblox.com/components/sib-chat/issues/99#note_26300

@balessan @sylvain @calummackervoy I'm splitting this one here.

Cool. We could also have one in the app for a quick workaround if we need.

mentioned in issue djangoldp#249 (closed)

Closing because we use ActivityQueueService to fulfil this. In fact though we retry until success or giving up

closed