Sakai currently has a considerable amount of messaging functionality, however it is diffuse and confusing. We have a NotificationService, an EmailService and an EmailTemplateService. We also have a BullhornService. One aim of this ticket is to coalesce these disparate pieces into a single service and update a single tool, Assignments, to use that service. This will be the first concrete step toward a unified User Messaging Service - once the approach is ironed out we'll create extra jiras to migrate other tools to use the single service. It will also make it far easier to update the Preferences tool to control this centralised resource.