It is better to use the global transormation unrolled all the way to the top node instead of local tranformation to the first mother volume
StiIstDetectorBuilder: A couple minor edits for consistency across StXXXDetectorBuilders:

- Switched to same names as in StiPxlDetectorBuilder
- Switched to natural numbering scheme as in StiPxlDetectorBuilder
Use the center sensor (or the one close to the center) to build the unified sensor layer in Sti - inspired by Hao Qiu
Split PXL sensitive layers in two halves. The change should help to avoid track backward steps in Sti due to ill ordered volumes in r and phi - inspired by Hao Qiu
StiXxxDetectorBuilder: Removed ionization from StiMaterial constructor as it is not used anywhere including energy loss calculations
StiXxxDetectorBuilder: Removed definition and addition of "hybrid" material because it is not used anywhere
StiXxxDetectorBuilder: Refactored gas material definition

For the gas surrounding the detector we use air properties as defined in global
geometry manager. If the AIR material is not available we use default hardcoded
properties
StiXxxDetectorBuilder: Refactored silicon material definition for sensitive layers

Only silicon material is used in construction of sensitive layers. As with the
gas we first try to use the material definition in the global geometry manager.
If the SILICON material is not available we use default hardcoded properties
StiSstDetectorBuilder: Refactored useVMCGeometry() to build sensitive Sti layers in the same way as in PXL and IST detectors
StiSstDetectorBuilder: Added a private method to split the SST mother volume into three tubes
StiSstDetectorBuilder: Model SST inactive material using the mother volume
StiXxxDetectorBuilder: Switched to StiMaterial constructor that accepts the radiation length as is. The desctription of the constructor is very poor but I think there is no need to multiply it by the density
StiSsdDetectorBuilder: Redefined StiMaterial for the segmented SST mother volume (SFMO). The values provided by Jason W.
Similar to PXL added flag to build ideal geometry for IST and SST. By default (buildIdealGeom = false) the database transfarmations are used in all StiXxxDetectoGroup-s