Provide Decisions objects for jets contributing to a jet hypo decision to pass an event
Jet hypos may be a tree of structure where the leaves test jet collections.
This MR is concerned with retrieving those jets that participate in passing the hypos, and the Hypo machinery which records these jets as participating jets.
Documentation on the start of this work is at tamartin/athena!1 (diffs)
Edited by Peter Sherwood