Neutronics improvements

[RemDelaporteMathurin]

• Don't pass materials both to the CSG cells and the Model objects
• in build_vault_model only return the geometry
• move baby_geometry() to libra toolbox
• use Geouned to convert CSG to cad and add it in the workflows
• include foils and detectors in the models (see Add Detectors and Dose tallies BABY-1L-run-1#10)