UC-99 Manually confirm fb users who don't have email addresses with fb

When a user connects via Facebook but doesn't have an email registered with Facebook (eg, if they registered using a phone number), we have them enter an email address for us to use. We want to have user's confirm those email addresses. If they come from Facebook, then we'll still auto-confirm them.

Ticket: https://wikia-inc.atlassian.net/browse/UC-99
There isn't a currently a case where this shouldn't be 'signup'. This class is only used inside of FacebookSignupController::createAccount. I think this was added to mirror the parent class which might receive different types, but UserLoginFacebookForm should only ever be 'signup'.