Bug 1005127 - [privacy] Add ability to delete profile

Works fine for me.
It required to add some new mixins, views and unit tests.
Using the url to determine the action isn't the best idea. Would it be possible to use some information about the user's state (i.e., something from `request.user`) to determine the correct path? Failing that, I'd prefer to add something to the context in the view such as at [1], rather than have logic in a template that relies on a url. Please choose one of those alternatives to this approach.

[1] https://github.com/mozilla/oneanddone/blob/master/oneanddone/tasks/views.py#L178