* fix :wrench: add unicode support in slug urls

* feat :star: add tests to check urls with unicode characters

Better to use filenames which are commonly used in the python word then
custom ones.

This allows updating code in both places, if necessary. Getting Django
1.5 support would be painful otherwise. This also removes the circular
dependency of django-oscar-testsupport on Oscar.

The requirements were merged. The imports were updated
accordingly. Unused imports in the touched files were removed. No
further changes.