* feat :star: optimize range products reordering

* test :white_check_mark: add test to verify range product reordering

* fix :wrench: remove local settings from test settings

* test :white_check_mark: update product reordering test

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

Latter one is deprecated

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.