add Shashlik to CaloTowers

[kpedro88]

This commit adds the Shashlik ECAL to the CaloTowers algorithm. It treats the subdet ID EcalShashlik as equivalent to EcalEndcap, passes the EcalRecHitsEK input tag to the algorithm, and specifies some preliminary thresholds equal to 1/2 of the current EB thresholds (based on a suggestion from Shashlik experts).

Validation of the changes, using runTheMatrix 13815 (QCD_Pt_600_800_8TeV with Extended2023SHCalNoTaper), plotting average CaloTower EM energy vs. eta:
old:

new:

[cmsbuild]

A new Pull Request was created by @kpedro88 (Kevin Pedro) for CMSSW_6_2_X_SLHC.

add Shashlik to CaloTowers

It involves the following packages:

RecoLocalCalo/CaloTowersCreator
SLHCUpgradeSimulations/Configuration

@civanch, @nclopezo, @mdhildreth, @cmsbuild, @StoyanStoynev, @slava77, @Degano can you please review it and eventually sign? Thanks.
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@fratnikov, @mark-grimes you are the release manager for this.
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[mark-grimes]

merge

All tests run fine. Not sure about the results but I guess that's what the relvals are for.