Initialization at start of run.  Get quantities from database
 which will be needed in event loop, and set other static variables
 to initial values.

 Decodes all the raw data and applies all the calibrations and BPM
rotations.. THEN it adds in a simulation, modifying the
 beam monitors to simulate dithering (depending on paramters)
 and then modifying detectors
 to account for beam position, beam current, and some noise
 This will also allow for faking the helicity signals

 Utility routine used by copy constructor and assignment.