Minor amendments in the HMS calorimeter part.

Changed column and row numbering in THcShowerHit.h in order to get rid of
warning messages on unsigned and integer comaprisons when compiling;

Corrected a debug message in THcShower.cxx.
Shower code: Editing of comments
Re-arrange, modify and make more detailed comments in the Shower*.h header
files. Add more comments in the Shower*.cxx files.