Write wrapper for dataloader returning perturbed datapoints

[GeoffNN]

I'd like a method similar to https://github.com/fra31/auto-attack/blob/67cdc76f0d5dd18af71958a739e10f90c0d1e787/autoattack/autoattack.py#L72

Things to pay attention to:

• Some arguments of the Adversary.perturb methods are datapoint and optimization method dependent.