Wired Actions::UpdateUser into UsersController.

Note that the controller specs for `#update` no longer test the
scenario where one registered user attempts to update the profile of
another. That's been rendered (nominally) impossible by the parameter
changes to the `Actions#UpdateUser` class from the earlier DSOs.

Note further that:

1. The only attributes that can be updated (as whitelisted by the
`Actions::UpdateUser#filter_user_data` method are `:email` and
`:profile`. Any other parameter values passed in are ignored and
removed;
2. There's a *ginormous* FIXME in `UsersController#on_update_success`
where the controller directly accesses the `UserRepository`'s DAO. Oops.

RSpec: 1020 examples, 0 failures, 94 pending
RuboCop: 249 files inspected, no offenses detected