Integration of the E\gamma Cluster Position Calculator into the PFClusterProducer

@jbendavid @ekfriis 

This PR incorporates the result of a study done that demonstrated improved cluster position resolution when the Particle Flow default electron/photon position corrections were replaced with the default E\gamma corrections.

The main improvement is seen in the ECAL endcaps, but there is some slight improvement for the barrel.

You can see the study here:
https://indico.cern.ch/getFile.py/access?contribId=0&resId=0&materialId=slides&confId=270535

I've @'d one of the Tau POG conveners since this should impact their particle-based reconstruction.
This should be followed up / checked out by the JME POG as well, but I can't find any of them on github.