Use email other than settings.DEFAULT_FROM_EMAIL

[mick-t]

Hi,

I don't want to use settings.DEFAULT_FROM_EMAIL as the email address that emails are sent from. I propose adding a settings option called REGISTRATION_FROM_EMAIL and if it exists RegistrationProfile._send_mail() & send_notification_email_reciver() will use settings.REGISTRATION_FROM_EMAIL and if it doesn't exist they will use settings.DEFAULT_FROM_EMAIL.

I will make the code changes and test and will do a pull request later today.

Thanks
--Mick