Returns column nr on which to split PSM table. Chooses from flags
    given via bioset and splitcol

def get_splitcolnr(header, bioset, splitcol):
    """Returns column nr on which to split PSM table. Chooses from flags
    given via bioset and splitcol"""
    if bioset:
        return header.index(mzidtsvdata.HEADER_SETNAME)
    elif splitcol is not None:
        return splitcol - 1
    else:
        raise RuntimeError('Must specify either --bioset or --splitcol')