Trigger modifications in the T0 monitoring setup

MR to help progress ATR-20006, but applicable to all trigger monitoring development.

• Enables configuration of dummy HLT trigger chains until we have JSON HLT menu configuration
• Tells TDT that it should expect R3 navigation (see https://twiki.cern.ch/twiki/bin/viewauth/Atlas/TrigDecisionToolMTFeatureAccess). Soon this will print either a warning or an error if the wrong type of call is made for features.

Marking as WIP as there is still trouble accessing the L1 XMLs. Works if manually copied into the run folder, but that's no good as a solution.

Ping @ponyisi & @ebergeas