DPG/PWGHF: monitor single-track efficiency from HF decays

[mfaggin]

@fgrosa @fcolamar @gluparel @scattaru @mmazzilli @deepathoms this should help for the analysis of Samuele.
I still want to add the same code for the case w/o grouping by mcCollisions, I'll add it tomorrow and then I'll open the PR

[scattaru]

Hi @mfaggin,
Thanks a lot for this update!

Cheers,
Samuele

[mfaggin]

In this PR I add the possibility to calculate the efficiency for tracks from HF decays.
This implied some changes:

• in processMC I needed to insert manually the loop over McCollisions grouping by hand the Collisions. This allows me to have the ungrouped McParticles table, avoiding unpredictable crashes in getCharmHadronOrigin (for b tracks, it might happen that the track is assigned to the wrong reco. collision, and if this collision belongs to a mcCollision different from the correct one for the beauty track and we work with grouped mcCollisions, then we miss the decay chain and the method fails)
• I also added the possibility to cut on the Z coordinate of the generated vertex (up to now, only a cut on the reco. posZ was applied)
• I replied the code in processMCWithoutCollisions. This duplication can be useful to study how the efficiency change if we ignore the track association to collisions (in processMC the efficiency is computed considering gen. particles only for reco. collisions, i.e beign a pure tracking efficiency indeed)

Tagging @fgrosa @fcolamar @scattaru @gluparel @deepathoms @mmazzilli in case they have further comments.
Tagging also @njacazio just to check whether I am not doing silly mistakes (btw from some check locally it seems ok)

[alibuild]

Auto-approving on behalf of @mfaggin.