We don't want two different accounts to exist with the same email
address only differing in case. This had already happened for a few
which have been manually fixed, since it turns out we only enforced the
rule on new account creation, not when accounts changed email address or
when they were created using oauth. Also add database level constraints to
make sure this cannot happen again if some codepath is missed.
"submitter", thus making it possible for a single person to manage
multiple organisations, as well as for a single organisation to have
multiple different manages.
Re-hook events and news items to use organisation of the submitter
instead of the user who did the submission. (product listings already
did this)
part of the core, since it seems like it could be useful for other
kinds of objects as well in the future, but for now only the
software catalogue uses it.
