Valuemaps for E/gamma GED Integration

Machinery to produce PFEG <-> GEDPhoton/GsfElement valuemaps needed for the final step of particle flow reconstruction. Don't expect much if any change in the physics output.

Preliminary tests on ttbar indicate the electron reconstruction takes a rather large chunk of time, will investigate further with igprof. 
The photon reco doesn't add much. 

@beaudett Would like to run a few more tests on his end and possibly change some configurations, but it would be useful to go ahead and start the process since the pieces are in place.

Short matrix results:
7 6 5 5 3 tests passed, 0 1 0 0 0 failed
The one failure is from an empty DBS query result for 8.0.