Ions pymask

[sterbini]

For ions the charge of the strong beam (BB lenses) should be multiplied by the Z of the strong beam species (for proton is irrelevant since Z=1).
This can be done with on_bb_charge but we would like to propose to add explicitly the convenient parameters in the config.py (for example the rest mass and charge of the weak beam and the charge of the strong beam).

[sterbini]

One need also to update accordingly the
pm.generate_sixtrack_input
to take into account the Z of the strong beam.