Python closure sampling

Created by: comane

Main modification: Level 1 data used for closure tests generated by validphys.pseudodata.make_replica instead of libnnpdf.experiments.MakeClosure. Closure tests no longer depend on the prepare_nnpdf_rng function which uses the c++ rng (see https://github.com/NNPDF/nnpdf/issues/1623 ). As a consequence "seed" and "rngalgo" are no longer needed in a closure test runcard, the random initializer only depends on "filterseed"