Bug 1005127 - [privacy] Add ability to delete profile

Works fine for me.
It required to add some new mixins, views and unit tests.
Ah, I get it. When you set the database up so that when a user is deleted it sets the TaskAttempt record's user field to NULL, I guess it interpreted that as being applicable to all of the other places where user is a foreign key. I don't think we need all of those changes. We may have to edit the migration manually.