Explicit (Phase-I) L1 thresholds for specific legs
Reestablishes the ability in the menu parsing to handle explicit L1 thresholds for multileg triggers. This is needed to disambiguate combined chains with e.g. egamma legs based on a muon-only L1 item.
The L1 thresholds will be checked against those provided in the
chainProp, with special handling needed for
muXnoL1 legs (must be seeded by FSNOSEED). Not (yet) tested for tau chains or chains including jets/xe.