StiIstDetectorBuilder: Yaping's changes
Updated in accordance with the nee pileup trees stucture.
Updated the instructions.
StiPxlDetectorBuilder: Don't proceed if the DB information is not available
StiPxlDetectorBuilder: Removed unused include
StiPxlDetectorBuilder: Got rid of redundant char array holding the volume's name. It also helps to have Sti volume names as close to the original TGeo ones as possible
StiPxlDetectorBuilder: No need to explicitly define individual volume instances in the list. The averaging procedure can create separate Sti volumes for all volume occurancies in TGeo