Trajectory cleanup -- rebase

Rebase of #3010.

Pure technical changes to cleanup Trajectory and TrackCandidate memory churn.
Still a lot can be done (for instance in Conversion code).
More will be done once fitters will be migrated to use standard TRH instead of TTRH.

In any case it is a sort of lost battle as classes whose objects are stored in vector in the event cannot be made non-copiable due to Reflex. Will try again with Root6.

No regression expected.
No regression observed.