[OzzModz] Allow Email Login Only 2.0.1

This is very good and ideally should be a default option imo in that the admin can force email only logins.

One slight benefit some might not actually realise is with an email only login, you can reduce any spam registration a bit, more accurately their posts as I've noted some of the older 'automated' spam post utilities rely on a username login (generally speaking, not XF specific) thereby having an email only login = spammer cannot login without human intervention = too much trouble for them in most cases. :)