Don't allow URLs in usernames or regular names

[mlissner]

A security researcher found that they can send emails like this one:

The way to do so is to put your username as www.evil.com. We should add some checks to make sure people don't do that. This also probably applies to CourtListener, and if we want to have some real fun, we could probably add it to Django as well.

The impact of this is really low, because users are super unlikely to click such a link, but it's worth fixing, sure, why not.

[mlissner]

I filed an issue in Django too: https://code.djangoproject.com/ticket/34763#ticket

If folks there want this upstream, let's just do that instead of fixing it here.