dRICH: add optics-debugging mode for testing trajectory reflection

• add debugOpticsMode 3:
  • all materials VacuumOptical except for mirrors and sensors
  • throw opticalphotons to help relate initial (normalized) momenta to sensor hits; this represents which sensors a track would hit, if the track were to be reflected off the mirrors
  • supports https://github.com/c-dilks/drich-dev/pull/4
• omit beampipe from drich_only configuration

compact/drich.xml

@@ -27,6 +27,7 @@
 <comment>
 - `DRICH_debug_optics`:    1 = all components become vacuum, except for mirrors; test opticalphotons from IP
                            2 = all components become vacuum, except for mirrors and `gasvol`, test charged particles from IP
+                           3 = all components become vacuum, except for mirrors and sensors, test reflected trajectories' hits
                            0 = off
 - `DRICH_debug_mirror`:    1 = draw full mirror shape for single sector; 0 = off
 - `DRICH_debug_sensors`:   1 = draw full sensor sphere for a single sector; 0 = off