Use the :occupied trait to mark a role as having appointments
Use the :occupied trait to mark a role as having appointments

`:occupied` sets up a role appointment with a date, so the code reuse is
nicer anyway; moreover, setting this the long way can fail due to the
relation being reset. (see also 4d9905c32)

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall