Backport evtgen photospp to7 1 x

This pull request depends on cmsdist pull #916. This request is being put in before the cmsdist patch at the request of Josh Bendavid Josh.Bendavid@cern.ch and Vitaliano Ciulli vitaliano.ciulli@cern.ch. Before merging please and for any question please contact them.  The pull request 4968 may have a small problem merging with ExternalDecayDriver.cc(h). Just use the one in the 4968 the only difference is the addition of lines.