Add 3FNS in default grids.

Created by: giacomomagni

Would it be possible to switch to a default grid in the evolution that starts from 1 GeV ? we should just adopt this grid as default:

https://github.com/NNPDF/nnpdf/blob/ce6c05cacec95dee36c577503c9a1109daa2908a/n3fit/src/evolven3fit_new/utils.py#L67

and change these lines:

https://github.com/NNPDF/nnpdf/blob/ce6c05cacec95dee36c577503c9a1109daa2908a/n3fit/src/evolven3fit_new/utils.py#L188-L194

This way all the uploaded fits, will automatically include IC in 3FNS and there is no need to do further work.

Thanks.

@RoyStegeman , @andreab1997 @scarlehoff