Allow internal cuts to be used within validphys 2

Created by: Zaharid

The idea is that cuts are computed internally by default, while retaining the options to use the fit ones and no cuts at all.

This will simplify running various things in validphys (one won't have to run vp-setupfit just to get the cuts for some data), and it will allow to use the cuts within vp-setupfit itself to compute the covmats with the right cuts.

One thing to decide is whether we want to have defaults for q2min and w2min somewhere or these should be always entered (I think no, since at that point it is worse than the fit based cuts). But that can be worked out later.

Closes #235 (closed).