Fix incorrect installation of CWL files

cwl_files = collections.defaultdict(list)
for dir in ('lofar-cwl', 'steps', 'subworkflow', 'workflows'):
    for file in glob.glob(os.path.join(dir, '**/*.cwl'), recursive=True):
        cwl_files[os.path.join('share', 'prefactor', os.path.dirname(file))].append(file)
data_files = cwl_files.items()

BTW: I do have a different implementation for lines 14-19 that doesn't use `os.walk`, but `glob.glob` instead. It's a bit slower, but maybe you consider it more readable: ``` cwl_files = collections.defaultdict(list) for dir in ('lofar-cwl', 'steps', 'subworkflow', 'workflows'): for file in glob.glob(os.path.join(dir, '**/*.cwl'), recursive=True): cwl_files[os.path.join('share', 'prefactor', os.path.dirname(file))].append(file) data_files = cwl_files.items() ```

The version with `os.walk` is fine with me -- though I did indeed misread it initially :)