For example, if we need to use a custom From: address,
we can now do:

    m = make_message("template-name", recipient, ctx)
    m.from_email = "...."  # customize here
    send(m)

- add optional `from_email` argument
- add test cases that exercise the retry loop

Planning to use it for sensitive operations (add/remove security keys),
change email, change password, close account.

The decorator sends a six-digit confirmation code to user's email
and renders a form for entering it back. If the user enters the
correct code, the decorators sets a sudo=active marker in
user's session, valid for 30 minutes.

When sending email using Django's default email
backend (SMTP), and if there is a network issue, the backend
can throw SMTPServerDisconnected.

This commit adds a retry logic which retries sending the
email two times when SMTPServerDisconnected is thrown.