Add email notifications for create, update, and delete events

[djperrefort]

The API endpoints can be easily extended to issue user notifications when create, update, or delete actions are taken against various records. Which notifications a user receives can be determined by user notification preferences.

Here are some suggestions for notifications off the top of my head. Group notifications are mostly intended for admins.

Record Type	Create	Update	Delete
Group		Yes	Yes
Grant	Yes	Yes	Yes
Publication	Yes	Yes	Yes
Allocation Request	Yes	Yes (specifically for approval)

Because the admin panel bypasses the API endpoints, this should be implemented after #300