This way we remove the duplication in the layouts which had these links.
Since we're now passing the `current_user` option to partials in all
cases, IMHO the code is easier to follow if we use the
`Layout::NotificationItemComponent` instead of its partial.
This way it's easier to refactor it.
Note we're using `with_request_url` in the tests because the component
renders the locale switcher, which needs a URL in order to work. This
doesn't affect whether we're in the management section or not.
