email notification - warning people when they're logged in about upcoming due dates, if they have email disabled, etc.

[botanicvelious]

1. bar at the top if notifications are disabled
2. bar at the top if behind schedule
3. affirmative opt in when registering and notifications disabled (student only?)
4. email gsoc admins ml if notifications turned off and a week behind

[terriko]

Closing in preparation for archiving this repo.