Fix untested StatusCodes exposed by gaudi/Gaudi!386
Touches HltSelChecker, DaVinciMCTools, DecayTreeTupleBase, JetAccessoriesMC, LoKiGenMC, ParticleMakerChecker, DaVinciTrackScaling, DisplVerticesMC, LoKiAlgoMC, LoKiPhysMC, LoKiExample
In addition some flyby modernisations:
- Remove some empty destructors
- Remove an obsolete Gaudi include
- Suppress compilation warnings from Boost