StiIstDetectorBuilder: Added flag to build ideal IST geoemtry
StiIstDetectorBuilder: We need to set the current gGeometry path before extracting any info about current volume position
StiIstDetectorBuilder: Yaping's changes
Merge branch 'ds-ist'
Updated in accordance with the nee pileup trees stucture.
Updated the instructions.
StiDetectorBuilder: Added method to remove a previously added Sti detector/volume
StiDetectorBuilder: Modified detector accessor to handle invalid detector requests in somewhat more graceful way
Uniform improvements in Sti objects output streamers
Remove unused variables
Added new data member to keep track of track energy losses in the node