Add autofocus to input fields of the Yesod.Auth.Email subsite

Note that this doesn't add autofocus to the login widget (since those are concatenated together for the login page).  

BTW, `Yesod.Auth.HashDB` does have autofocus for its input field: https://github.com/yesodweb/yesod/blob/master/yesod-auth/Yesod/Auth/HashDB.hs#L228