Ecal regression refactor

This code refactors the ECAL regression inputs so a new single class gets the data rather than the same (buggy) code being copy & pasted over 3 files. It also fixes a divide by zero bug. It changes the behaviour of the pat::Photons but for the better in my opinion. 
You have a point. Think about it, I leave to you to decide which is more proper and elegant (not a big issue as you said).