Make the NotificationActor scalable

(Missing Feature, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Scalability
Summary: Currently, it's a singleton, so that clearly must change.
Do we need this Actor at all? Could we simply eliminate it? It seems like it's not doing anything that couldn't be delegated to other Actors that are more scalable, like the UserSession.