Get the type of the tomodir and the highest iteration to list all files,
    which will be plotted.

def list_datafiles():
    '''Get the type of the tomodir and the highest iteration to list all files,
    which will be plotted.
    '''
    is_cplx, is_fpi = td_type()
    # get the highest iteration
    it_rho = read_iter(is_fpi)
    it_phase = read_iter(False)
    # list the files
    files = ['inv/coverage.mag']
    dtype = ['cov']
    files.append(it_rho)
    dtype.append('mag')
    if is_cplx:
        files.append(it_rho.replace('mag', 'pha'))
        dtype.append('pha')
    if is_fpi:
        files.append(it_phase.replace('mag', 'pha'))
        dtype.append('pha_fpi')

    return files, dtype