Django-ordered-model

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- Drop support for Django < 1.11

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- Add support for Django 2.0
- Fix problem where swap took a queryset instead of a model instance

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- Fix a problem with links in the admin when using multiple threads.

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- Use Django's version of `six`
- Fix various deprecations
- Fix missing up/down links with custom primary key

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Fixed

- `pip install` not working due to missing `requirements.txt`

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Added

- Support for ordering using a specified base class when using Multi-table inheritance
- Suport for Python 3.6, Django 1.10 and 1.11.

Fixed

- The move up/down links in OrderedTabularInline
- Passing args to `filter()` which broke django-polymorphic.