StiXxxDetectorBuilder: Instead of setting StiDetector parameters in a local private method switched to using new interface provided by StiDetector

The refactoring takes place for both sensitive and inactive volumes
StiXxxDetectorBuilder: Removed output debug messages as they can be easily replaced by a single call to StiDetectorBuilder::Print()
Do not set StiDetector members _key1 and _key2 as they are not really used anywhere