Xcoll release 0.7.2

Develop Updates

• Remove dunders from setting names in Constants to avoid incompatibilities with core Python name-mangling
• Adapted prebuilt kernel definitions to include EXTRA_XCOLL_CLASSES
• Better GEANT4 compilation and environment checking
• Wrap run(['which', ...], ...) in try.. except to avoid failing on systems where which is not installed
• Pre-compilation of Geant4Collimator works, however, leads to segmentation fault when running. Might have to do with pybind11 dependency.Temporarily removed from perbuilt kernels.

Full Changelog: v0.7.1...v0.7.2