Backport of PF-Mustache SuperClusters / electrons seeds from 700

NB: The regression is turned off for the mustache SCs!
I wasn't able to use runTheMatrix.py in CMSSW_6_2_0_SLHC7, if fails on a key-error for some workflow that's missing. I am submitting this untested, sorry for the trouble, all of the things that are backported have of course been tested in 700.

Expect big (but correct/expected) changes in shower shapes for PF-based ECAL super clusters.
Electron efficiency shouldn't change much, PF-ECAL supercluster efficiency and resolution will change quite a bit.

Regression is turned off since it isn't in the GT for 62X_SLHC, and really shouldn't be. 
It doesn't affect seeding efficiency.