Phase-2 Calo: e/g standalone emulator & related objects

[cerminar]

Following the discussion we had during the integration of PR #1069, I report here a few comments that I expressed in that occasion:

1. The 3 "digitized" classes only persist an integer. Therefore, it would be more convenient to store them within the corresponding CMSSW object to ease their access by downstream consumers.

• The DigitizedClusterGT objects should become a data member of the CaloCrystalCluster or the Egamma objects (most likely the second since we will need a digitized word also for the HGC sector).
• Same goes for the DigitizedClusterCorrelator and DigitizedTowerCorrelator, which should become data members of the CaloTower objects.

2. We need to add the quality bits to the DigitizedClusterGT; otherwise, they can not be consumed by either the GT nor the Correlator emulators

3. We need to establish a link between Egamma and CaloCrystalCluster, possibly via an edm::Ptr<L1Candidate>. This would allow doing the same with the HGC multiclusters once added to the emulator.