Passing Detector Info/Material Info into Chroma

[twongjirad]

Write virtual python base class that user implements. The user implemented functions provide location of GDML and COLLADA file, provides mapping between RAT/GDML sensitive detector indices and that of Chroma. Also passes optical property data to Chroma. Probably can do this using some sort of parser.

This all then needs to get packed up in a protobuf message to the Chroma Server.