allowEmails used to always be set to true and did not use
can_invite_via_email, which checks for enable_local_logins.
It was a problem because on sites with local logins
disabled users were allowed to enter email addresses, but
received a generic error "error inviting that user".
This is where they should be as far as ember is concerned. Note this is
a huge commit and we should be really careful everything continues to
work properly.