extract to `plan_selection#to_attendee_plan`
comm
move the airport fields out of attendee params ..

.. so that we don't have to clean them up later to avoid mass assignment errors
temporarily hide the admin fields, which are not submittable right now
increase negative space above footnote
abandon all hope of nesting the attendee routes

Nesting `attendees#new` and `#create` did not work out because `form_for` generates the wrong url for the form `action`.  In hindsight it seems obvious that splitting up your routes, half nested, half not, is asking for trouble.