[download] rename list_folders to list_dir

MANIFEST.in

bob/extension/data/test_list_folders/README.rst

bob/extension/data/test_list_folders/database1/README1.rst

...ension/data/test_list_folders/database1/protocol1/dev.csv

...sion/data/test_list_folders/database1/protocol1/train.csv

...ension/data/test_list_folders/database1/protocol2/dev.csv

...nsion/data/test_list_folders/database1/protocol2/eval.csv

bob/extension/data/test_list_folders/database2/README2.rst

...ension/data/test_list_folders/database2/protocol2/dev.csv

...nsion/data/test_list_folders/database2/protocol2/eval.csv

...ension/data/test_list_folders/database2/protocol3/dev.csv

...sion/data/test_list_folders/database2/protocol3/train.csv

bob/extension/data/test_list_folders1.tar.gz

bob/extension/data/test_list_folders2.tar.gz

bob/extension/download.py

bob/extension/test_download.py

doc/py_api.rst