Micro from700 reduced egamma

Implement a comprehensive slimming and relinking of electron and photon collections through a dedicated producer.  This removes the duplication of embedded cluster information between electrons and photons.

Reduced conversion collections (with loose matching) are also produced.

Stored information is not exactly the same as before (can be tweaked further).

Current selection is
 keepPhotons = cms.string("pt > 14 && hadTowOverEm()<0.15"),
 relinkPhotons = cms.string("(r9()>0.8 || chargedHadronIso()<20 || chargedHadronIso()<0.3*pt())"),
 keepGsfElectrons = cms.string(""),
 relinkGsfElectrons = cms.string("pt>5"),

The "keep" selections control which objects are stored.  The "relink" selections control for which objects the dependent clusters/rechits/conversions are to be stored in the associated reduced collections and refs relinked.

Contrary to before, the SuperCluster and seed cluster are only included if the "relink" selection is passed.  (The last configuration for embedding was keeping these for all.)

There is additional information being stored through the conversions, and also the preshower clusters/rechits which were not included previously in the embedding.  (Can be discussed if this is really needed).

Net effect on event size is a minor (1.5% total) reduction for ttbar and essentially no change for jetHT data.  (Attached are edmEventSize dumps)

(I see that it won't merge automatically due to the last change in the configs, will rebase it tomorrow)