Track multiple email addresses for an organisation

Track multiple email addresses for an organisation

This allows organisation managers to add more than one email address to
an organisation, and use this for sending news from. Sending news is the
only thing that the email field is used for at this point. Adding an
email will trigger a validation email sent to the address with a token
to confirm it, so that we can actually trust the emails.

Remove the previous registered emails on organisations. These addresses
were never validated and thus cannot really be trusted, so it's better
to remove them cleanly than to migrate them into the new system and be
uncertain.

Finally, in passing, remove the phone field on organisations. We've
never used that for anything and there's not really any point in
collecting the data.