GeoModelHelpers -- Introduce cloneVolume
Introduce new function to clone physical volumes.
- If a fullphysical volume in the subtree is detected, then a clone of the volume is made
- Otherwise, it's steered via the boolean argument
The question is what are we doing with the clone methods of the GeoPhysVol & the GeoFullPhysVol. They don't have this detection mechanism. I'd propose to remove them