Resolve "dRICH: increase z-length, and add space for services"

Closes #18 (closed)

• see issue for more details

Changes to definitions.xml relevant for other detectors:

• add constant ForwardPIDRegion_rmax for the PID region; this is used to define a new radial service gap between the PID region and the barrel HCal
• the new service gap pushes HcalBarrel_rmin to 195 cm (see Roland's slides, linked in #18 (closed))