Add `perturb` command, to perturb initial conditions.

[atteggiani]

A useful task for researchers is to perturb the initial conditions of an experiment that sometimes might crash for instability reasons.
A version of a perturbation script can be found in /projects/access/apps/pythonlib/umfile_utils/access_cm2/perturbIC.py.

This script can be updated and upgraded to be embedded in the amami interface.