CP algorithms: Add simple ability to store calo cluster eta for egamma particles

I am a bit conflicted about this one. I wanted a simple ability to store calo cluster eta for egamma particles as this is a very common requirement. We already have a special block for photons which sounds a bit too much so for now I added an algorithm that runs very early in the calibration sequence and is toggleable with a flag. For now the existing photon behaviour is kept but both can not run at the same time (as they overlap).

/cc @tstreble @ravinab @jedebevc