Replace 'assert' with 'assert*' method.

Convert tests.unit.forms.widget_tests to use TestCase class.

Convert bankcard tests to use TestCase.

Convert tests.unit.logging_tests to use TestCase.

This also removes the attr() marking of tests. This can be implemented
in pytest with marking the tests with a custom marker if required.

Fixes #1399

See https://gist.github.com/codeinthehole/6178034 for some discussion.

Use field validators and model clean methods instead of forms.

Include new methods for voting up and down.

Add more tests.

Methods like clean_title don't get called dynamically.  Have moved
cleaning logic to the form which seems a more natural place.

Introduce some new test folders.

By adding the __setstate__ method an infinite loop is avoided regarding
the use of __getattr__ on the ProductAttributesContainer model.

Moving tests into appropriate folder

...as they are all integration tests (they save stuff).