Make Perturber inherit from LitModular

[dxoigmn]

          Why can't this be a `LitModular`? Then we inherit all of the optimizer functionality. The problem, I think, is the modules functionality. However, that should, in theory, cleanup the use of objective and gain since we can treat them as modules?

As I thought about this more, it would be really nice for this to be a LitModular because then this code could be used to generate attacks using the Lightning framework. That is, we could run the validation loop to test the efficacy of the attack after every epoch and run the test loop at the end too.

Originally posted by @dxoigmn in #103 (comment)