Allow optional inputs in Allen
Adds the ability to make inputs to Allen algorithms optional.
This is needed for Allen!521 (merged). In the default pp configuration, the Allen SelReport writer runs for all events regardless of GEC decision but needs reconstructed objects to create SelReports for events that pass the GEC. If the reconstructed objects are not optional, the reconstruction will run for all events, regardless of GEC decision.
Edited by Thomas Boettcher