Add VPVolumeID class for converting between DD4hep volume IDs and sensor numbers

In GetTrackerHits::fillHit in Gauss, the MCHit sensitive detector ID is set to the G4 detector ID, which in turn has been set to the DD4hep volume ID. As such, we will need to be able to convert easily from the DD4hep volume ID back to quantities like the sensor number, module number etc. In particular this will be needed in VPDepositCreator::createDeposits in Boole. This MR adds a class VPVolumeID to perform that conversion.