Make UnassignedPersonPresenter return false for present?

Also check for primary_role.current_person in the view as the role is
present but not filled.

https://www.pivotaltracker.com/story/show/45903741
replace current_person.present? with has_appointment?

Also change the view logic
Merge pull request #408 from alphagov/worldwide-org-people-list

Do not show the people header on ww orgs when there are no people in roles

https://www.pivotaltracker.com/story/show/45903741