Combining a couple of issues for writing nice reusable mail and command classes.

We need iterative email commands to handle the following situations. Implement all with commands.py, and put emails in a subdirectory within templates/emails.

• When clearing rooms at the end of a semester.
• Before a semester, reminding people to set their rooms.
• In case of a security breach or another critical matter where we need to contact everyone.

See the implementation in accounts/views under DeleteStudent as an example of how to send a list of emails through the server. Setting all rooms to None for the first scenario is already implemented, though without the additional email blast.

For the first two scenarios, remember to let students know they can delete their accounts if they are no longer attending Mason.

All of these emails we should send out to students regardless of any as-yet-to-be-implemented inbox preferences, so don't worry about any configuration on the student's end. These are of sufficiently high importance and at a low enough frequency that people can deal with getting them without encountering legal issues over spam.