Add ThcSignalHit class

Follow SRC model and make a scintillator plane class.

TClonesArray ConstructedAt method.

Raw hit class for drift chambers and skeleton drift chamber that prints
out drift chamber package hits.

Move Compare method from THcHodoscopeHit to ThcRawHit since it should
work for any derived class.

Get detector name -> ID mapping from the map file comments

THcHodoscope, a multiplane scintillator array.  Make a Hall
C style spectrometer (so that default Hall A detectors are not
included.)  Can read a Hall C data file and print out hodoscope hits
where the left/right TDC/ADC are matched up per counter.