Support Django 1.10 style middleware

[mikix]

In Django 1.10, a new middleware style was introduced, that uses a MIDDLEWARE setting rather than MIDDLEWARE_CLASSES.

In Django 2, only the new style will be supported.

This change allows our middleware to be used both ways, but drops support for Django 1.8.

This package claims to support Django 2, but the current middleware classes can't work with Django 2, right? Was that ever tried?

If Django 1.8 support is important to maintain, I can do an optional import situation and keep support. But I figured the open edx ecosystem is on 1.11+.

Reviewers:

• [ ] @edx/arch-review
• [ ] tag reviewer

Merge checklist:

• [ ] All reviewers approved
• [ ] CI build is green
• [ ] Version bumped
• [ ] Changelog record added
• [ ] Documentation updated (not only docstrings)
• [ ] Commits are squashed
• [ ] PR author is listed in AUTHORS

Post merge:

• [ ] Create a tag
• [ ] Check new version is pushed to PyPi after tag-triggered build is finished.
• [ ] Delete working branch (if not needed anymore)

[mikix]

I haven't tested yet with a new-style repo. I'm trying to do that with course-discovery now.

But the change should be harmless. We're doing it elsewhere: https://github.com/edx/edx-drf-extensions/commit/84cf1de98338d6a5f11e26158481c2158005151c

But will try to set up a course-discovery PR that points to this branch.

[mikix]

https://github.com/edx/course-discovery/pull/2011

^ That seems to work with this branch. And I also manually tested that still using MIDDLEWARE_CLASSES with this branch continues to work.

[mikix]

Oh I did update the docs in this PR

[robrap]

Oops. Not sure how I missed that. Thanks.