Email change bug - confirmation email message is superfluous

[jogwen]

Fixed #121 by re-generifying the email message, email confirm screen and success message so this is now a lot less confusing for users when they change their email address on their account!

However, I still think there's a bug here because confirming the new email has no effect - the user account's email address was already changed on form submit. Also, need to send confirmation link to old email address, not new email address, to check ok to change. Consider fixing and submitting as pull request to django_user_accounts.