Django-oscar

- Drop Django 1.9 support.
- In offer group list, dim inactive offers and vouchers.
- List related vouchers on benefit and condition edit pages.
- Limit orders displayed on voucher stats.
- Start testing against Django 1.11 and Oscar 1.5rc1:
- Fix issue with Voucher ordering when doing a
select_for_update. - Fix Oscar 1.5 issue with conditionaloffer_set vs offers
related name. - Fix Oscar 1.5 issue with basket.Line.line_tax. - Upgrade sandbox to Oscar 1.5.
- Add new field to ConditionalOffer: short_name
- Make OfferApplications ordered

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* Support Django 1.6
* Templates now load assets over HTTPS where appropriate

- Add concept of Offer groups.
- This makes it possible to create promotions which overlap on
line items.
- Add API for determining why a line was discounted.

- Improve unit testing with tox.

- Upgrade test dependencies.

- Upgraded to `versiontag` 1.2.0.