Merge pull request #7 from dimagi/email-is-not-a-login

don't include email in the list of valid logins as this isn't unique
Revert "don't include email in the list of valid logins as this isn't unique"

This reverts commit 752e2496e06eeb53b5c68b7f92805e8c656c936c.
add no-email backend and fix tests