Apply regression corrections from database in PFECAL-SuperClusters, decrease PF-SC seeding thresholds

This branch includes an update to apply a BDT regression to found PFECAL-SuperClusters in an event.
The penalty to timing is marginal, about 0.003 seconds are added for this module per event in the ttbar sample.

We should see improved energy resolution for superclusters associated to electrons and photons.
Not sure of the impact on soft clusters.

The associated .db file will be moved into databases soon, for now it reads from a local file. This will be changed once it's in the GlobalTags.

This PR is also pending some final validation from the developer of the regression weights.

Also:
barrel seeding threshold goes from 3 GeV to 1 GeV
endcap seeding threshold goes from 5 GeV to 1 Gev
There is a corresponding increase in superclustering timing.