Edx-organizations

See [ADR 1](https://github.com/edx/edx-organizations/blob/master/docs/decisions/0001-phase-in-db-backed-organizations-to-all.rst) for context.

In this PR, we add four new API functions to support the phase-in of database-backed organizations:
* `is_autocreation_enabled`
* `ensure_organization`
* `get_course_organization`
* `get_course_organization_id`

There are no breaking changes in this release. A follow-up release (6.0.0) with breaking changes will be necessary.

* Added Python 3.8 support
* Removed Python 2.7 support
* Removed Django < 2.2 support

Squash migrations in preparation for Juniper release.

- Adds support for Djangos 1.11-2.2.
- Use `pycodestyle` instead of `pep8`