Draft: IRT integration for eRICH

NOTE: most likely this MR will be closed, in favor of using Juggler geometry service directly

• start integration of IRT code
• for now, some IRT code is hacked into the geometry source file, controlled by macro IRTGEO; later we can consider using the TGeoManager output (from dd_web_display, for example), so we don't need to rely on preprocessor conditionals, as long as all required information can still be found