Sorts `similarities` and return the indexes in pairs ordered by highest similarity.

def sort_idxs(cls, similarities):
        "Sorts `similarities` and return the indexes in pairs ordered by highest similarity."
        idxs = cls.largest_indices(similarities, len(similarities))
        idxs = [(idxs[0][i], idxs[1][i]) for i in range(len(idxs[0]))]
        return [e for l in idxs for e in l]