Saved current StiIstDetectorBuilder in order to by maintain 100% backward compatibility

The user may choose to construct the IST detector with the older version by simply propagating an option to
StiIstDetectorGroup. StiIstDetectorBuilder1 inherits from StiIstDetectoBuilder to avoid duplicate code. Removed
implementation of inherited methods and other irrelevant declarations
StiIstDetectorGroup: Added parameter to choose IST detector builder

This is justified by the requirement of backward compatibility. The user can
choose the appropriate option in case there is a need to reconstruct the data
using an older detector builder
StiIstDetectorBuilder: Removed methods which will not be used by the new builder
StiIstDetectorBuilder: Do not print out transformation matrix for built sensitive layers in Sti
StiIstDetectorBuilder: Append new Sti detectors to the end of detector container, and use ladder id to index sector slots
Removed warning for extremely unlikely exception when a new StiDetector is not constructed by Sti detector factory. Such situations need to be treated in a way other than simply issuing a warning
StiIstDetectorBuilder: Removed pointless assert
Removed never used variable, forward declarations, and header includes
Minor stylistic changes for consistency across PXL, IST, and SST detector builders
StiIstDetectorBuilder: Defined placement for sensitive IST layers in a way consistent with PXL and SSD detector builders
StiIstDetectorBuilder: Fix loop over ladders since we use human friendly numbering starting with 1
StiSstDetectorBuilder: Changes helper function declaration to static
StiIstDetectorBuilder: Made buildInactiveVolumes() method inheritable
StiIstDetectorBuilder: Added a couple of helper methods to ease manual construction and placement of inactive volumes
StiIstDetectorBuilder: Implemented simplified Sti geometry for inactive material in IST