Update MCEvent with version from DaVinci v38r1p4
Patched back from the GitLab merge request LHCb/!430 (merged) directly into the code, since simpler than cherry-pick'ing and solving conflicts.
Edited by Marco Cattaneo
Patched back from the GitLab merge request LHCb/!430 (merged) directly into the code, since simpler than cherry-pick'ing and solving conflicts.