LP#1879983: make fetch_{staged,arrived,delivered} return holds

LP#1879983: make fetch_{staged,arrived,delivered} return holds

This allows the corresponding tabs in the staff user interface
to display the list of items, allowing for better error-checking
by staff.

In the case of fetch_delivered, a heuristic is used: holds that
have been marked fulfilled at the appointment's pickup library
within 90 seconds of the appointment's delivered timestamp
are included.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>