Django-userena-ce

- Increased max_length of the language codes to 8 to support BCP47. If you use
`UserenaLanguageBaseProfile` with `zh-Hans` or `zh-Hant` you will need to create
a new migration and apply it.

- Dropped support for Django 1.11 as `django-guardian` has dropped support for Django 1.11 from guardian 2.0 onwards.
Users who need to stick with Django 1.11 and/or python 2 will need to use `django-userena-ce<5.0`.
- Dropped support for Python 2.7, 3.4, and Django 2.1 as these are end of life.
- Added support for Python 3.8 and Django 3.0.

- Moves the zh_CN and zh_TW locale directories

- Adds support for Django 2.1 and Python 3.7
- Note: you will probably need to generate a migrations for concrete implementations of `UserenaBaseProfile` and `UserenaLanguageBaseProfile`
- Replaces `userena.views.signout` with the class based `userena.views.SignoutView`
- Adds request argument to `userena.backends.authenticate`

- Drops support for Django 1.8
- Fix security issue of leaking password reset token through the Referrer (bread-and-pepper/django-userena/548)
- Removed deprecated `userena.utils.get_user_model()`

Added support for Django 1.11 and Django 2.0, dropped support for Django 1.9
and Django 1.10.

This is the final release that will support Django 1.8.