Draft: iterated hamming-distance perturbations greedy experiments

Function iter_hamming_distance_perturbed_greedy(), which is called along with greedy() in serverID.py. The prediction results of various trials are saved to CSV files and plotted (saved as images in specdir of demo).

Rebased version of !1736 (closed); reuse of functions random_digit() and perturb_student_id().

Note: is slow because conversion to NumPy arrays is not yet in place.