python: Reorder imports with isort

setup.py

swh/lister/__init__.py

swh/lister/bitbucket/__init__.py

swh/lister/bitbucket/lister.py

swh/lister/bitbucket/models.py

swh/lister/bitbucket/tasks.py

swh/lister/bitbucket/tests/test_lister.py

swh/lister/bitbucket/tests/test_tasks.py

swh/lister/cgit/__init__.py

swh/lister/cgit/lister.py

swh/lister/cli.py

swh/lister/core/indexing_lister.py

swh/lister/core/lister_base.py

swh/lister/core/lister_transports.py

swh/lister/core/models.py

swh/lister/core/page_by_page_lister.py

swh/lister/core/simple_lister.py

swh/lister/core/tests/test_abstractattribute.py

swh/lister/core/tests/test_lister.py

swh/lister/cran/__init__.py