Investigate failures to visualize Union endcap components

[spradlin]

          I would like to bring this to a close by visualizing each of the endcaps.  However, when i try to visualize the endcaps for any of the geometries that have an ExtraTower, the plug section of the cap does not display and i get the following error:

ERROR: G4VSceneHandler::RequestPrimitives
  Polyhedron not available for WCTopCap
  Touchable path: expHall 0 WCBox 0 WCBarrel 0 TopCapAssembly 0 WCTopCap 0 
  This means it cannot be visualized on most systems (try RayTracer).
  1) The solid may not have implemented the CreatePolyhedron method.
  2) For Boolean solids, the BooleanProcessor, which attempts to create
     the resultant polyhedron, may have failed.
ERROR: G4VSceneHandler::RequestPrimitives
  Polyhedron not available for WCTopCapBlackSheet
  Touchable path: expHall 0 WCBox 0 WCBarrel 0 TopCapAssembly 0 WCTopCap 0 WCTopCapBlackSheet 0 
  This means it cannot be visualized on most systems (try RayTracer).
  1) The solid may not have implemented the CreatePolyhedron method.
  2) For Boolean solids, the BooleanProcessor, which attempts to create
     the resultant polyhedron, may have failed.

For example, here is a visualization of the Top endcap of the HyperK_HybridmPMT_WithOD geomety without the ID PMTs displayed and with some of the barrel border cells set to invisible:

I suspect that the Boolean construction of the cap plug and cap black sheet cannot be rendered. I do not know why. However, i think that should be followed up in another issue.

I also think that the investigation into the stopped particles should also be spun off into a separate issue.

And i think that the notes of this investigation into overlaps, and its accompanying merge request, is ready for review.

Originally posted by @spradlin in https://github.com/spradlin/WCSim/issues/24#issuecomment-1520503043