Nudge/alert user via push who is offline
From a user ()https://rink.hockeyapp.net/manage/apps/34560/feedback/21251)
"Also, be nice to send a manual alert notification to a user (who allow the feature) who is either offline/online. This would be like an attention or nudge notification. If a user was offline and changes to online he would get this "nudge" and realize that the >contact has something that needs his attention."