Data cuts should be usable within validphys

Created by: Zaharid

I would like that use_cuts defaults to True (which is not a breaking change) and computes the cuts by itself, using #181.

Technically this is breaking compatibility because the cuts we compute are potentially different from what is stored in the fit, which we would be using now, but I don't think I really care. We should however probably have a new mechanism for reading the filter cuts.