* Use entire queryset for offer report download rather than paginated queryset

* Add offer order report test

* Specify order number in create_order factory

* fix :bug: remove combination offer in both offers

* feat :star: add test to check offer removal from combinations

- allow creation of offers of all types
- allow creation of vouchers with multiple offers
- allow creation of voucher sets of all usages, and with multiple offers

The priority isn't strictly a "restriction", but this seems like the most sensible form to add it to.

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.

Following guidance from Tangent's UX team (blame them!)

* Split 'metadata' step into 'name and description' and 'restrictions'
* Add progress bar
* Add summary of entered data in right-hand sidebar
* Clean up breadcrumbs and URLs

Still needs from FED love.

Fixes #376

Also split them into unit and functional tests.