Allow creating accounts before-hand

[sumanthratna]

one-time link (like Gavel) or one-time password

might be hard to do w/ allauth?

means we don't have to wait for judges to create accounts...also means we can skip admin approval since an admin would be the one creating accounts

https://github.com/aaugustin/django-sesame, pennersr/django-allauth#2438 (comment)