Before this change, it was conflating WebTest functionality with the
Django test client. This change removes the Django test client
functionality (namely, the login function which was being automatically
called).

A shed-load of tests are adjusted to work with this change.

This almost completes the work for #826 - only a couple more references
to the Django client are left in the test codebase.

ClientTestCase is deprecated.

Fixes #826
Fixes #1007

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.

Fixes #376

Also split them into unit and functional tests.