Fixing issue #56

[VinzenzBildstein]

• Added map to DetectorConstruction that holds the new struct DetectorProperties (mnemonic, systemId, detectorNumber, and crystalNumber).
• Map is populated at BeginOfRun function (which calls DetectorConstruction::SetProperties()) via examining all daughter volumes of the world volume.
• Changed names of SPICE and TRIFIC detectors to include '_' between name and instance number.
• Removed parsing of volume names from the stepping action.
• Replaced custom particle type with PDG encoding.

The last point might create the need for some changes in programs that process the simulation data!