The setup has five parts:
- a new email template type
- a new django-q task for notifying
- a management command for scheduling the task periodically
- a new settings variable NOTIFIER_LIMIT for controlling the number of
  days into the future the notifier script should use for end date of
  roles.
- a new settings variable NOTIFIER_SCHEDULE_TYPE for controlling how
  often the notifier task should be scheduled when using the management
  command.

Resolves: GREG-162

Issue: greg-112

The Role model has a not null constraint on the sponsor field, so it is
impossible for a Role object to not have this attribute.

Introduced to make editing of templates possible using the admin
interface. There are currently two types of templates, and there can
only be one instance of each type so that the system knows which
template to use in which situation.

Resolves: GREG-73

Isuse: GREG-66

Issue: GREG-42

Issue: GREG-42

Issue: GREG-42