Printout functions interface

[jncots]

All event generators have some sort of printout functions for an event, e.g. dt_evtout in DpmJet or sib_list in Sibyll. Since EventData class may contain transformed momenta and energy, it would be good to have a direct access to raw data produced by event generator for debugging.

I have in mind to write a method for "MCRun" which would return the output of the printout functions as a string. Here I would like to discuss whether this functionality is needed and in what form.

A related issue: probably EventData class also needs a listing similar to dt_evtout output?