Small Shower Calorimeter corrections, chagnes and cleanups

Make matched cluster variables of the array part of calorimeter private.

Initialize fY variable in the THcShowerHit::THcShowerHit default
constructor.

Correct typo in THcShowerArray::Clear, assign -1000 to fMatchClY.

Edit debug output in THcShowerArray::CoarseProcess and remove obsolete
comments THcShowerArray::MatchCluster.

Clear fSizeClustArray and fNblockHighEnergy quantitites in
THcShower::Clear, for just in case.