This is done via a custom PATCH due to the lack of transactions of MongoDB;
we cannot undelete both project-referenced files and file-referenced
projects in one atomic operation.
/join should only be used when someone can actually buy a new subscription.
/renew should be used when someone already has a subscription that needs
to be renewed.
Since url_for('cloud.xxxx') makes no sense in Pillar, I just hard-coded
/renew instead.
