Investigate: MpdGetNumEvents class - refactor or get rid of completely

The file also contains MpdLibZ class which is used only in MpdGetNumEvents.
It contains static methods GetNumXYZEvents where XYZ is generator type.
These methods seem to be formally used in runMC.C since "Init repo" commit, and we should investigate whether they are needed at all.

EDIT: the parameter nStartEvent in runMC.C is actively used. The desired functionality - reading a gz file and getting total number of events - must be redesigned.
Identified issues so far

• MpdLibZ class is code bloat (imo it is not needed)
• the enum EGENERATORS is not used (and should be), instead we have XYZ static methods (what is this obsession with using static all around the place)
• pretty much everything should be kept in a single method taking 2 parameters - filename and EGENERATORS enum
• C++ iostream must be used instead of C