Adding SM Z decaying to 3 photons UFO to MadGraphModels.

Add SM ZAAA UFO model to MadGraphModels for dedicated 3 photon search. We have used this UFO for 8 TeV search for multi-photon analysis. We also are requesting a MC sample of this process, with Exotic group with JIRA ticket: https://its.cern.ch/jira/projects/ATLMCPROD/issues/ATLMCPROD-8060?filter=allopenissues

The 8TeV paper is here: https://arxiv.org/abs/1509.05051

Analysis contact: James Beacham j.beacham@cern.ch and Pingchuan Zhao pzhao@cern.ch Exotic group contact: Samuel Meehan smeehan12@gmail.com and Patrick Rieck patrick.rieck@cern.ch