Add utf-8 support in slugs with autoslug

Slugs end up empty if list name consists only of non-ascii characters
and that results in an error. Autoslug converts non-ascii characters to
appropriate ascii ones and auto-updates the slug when list name changes.

Add unidecode dependency and fix PEP8 errors

models.py: add one blank line for PEP8

setup.py

@@ -99,6 +99,7 @@ setup(
     include_package_data=True,
     zip_safe=False,
     tests_require=['tox'],
+    install_requires=['django-autoslug', 'unidecode', ],
     cmdclass={
         'clean': Clean,
         'test': Tox,