INCR-479

Added the import statements

INCR-481

REVEM-289: Discount no previous purchase

INCR-459: Run python-modernize and isort

Split common/lib/chem into separate repository

Upgrade djangorestframework and install drf-yasg to get better OpenAPI support

Unpin gunicorn.

INCR-473: Make compatible with Python 3.x

Only make users who haven't previously enrolled in a non-upsellable course eligible for the discount

Defaults to common.py lms (OPS-4041)

Fix templates for XSS code injection via translations

This would patch all templates (django/mako)
for a possible XSS code injection via
translation files by html escaping them..

LEARNER-4632

WL-1492 | Remove arbitrary code rendering on course about page

Check if enterprise matches site before consent

We don't support enterprises with catalogs that span sites, so we can
safely ignore checking for consent when the site a learner is viewing a
course in is different than the enterprise that the learner is linked
to.

Ensure that exam due dates reflect course pacing

Removing flaky tests

Add CSRF_TRUSTED_ORIGINS settings

remove staff exemption from the library_content transformer

These were originally fixed individually, but had to be reverted, and
are now combined in one commit.  The originals were:

7b9040f6 This enum was backwards
8774ff1f Use ref_name to disambiguate serializers that drf-yasg would otherwise assume are the same.
8a443971 Is this field missing because it is None?
4a1154a7 Give a safer buffer for clearing the rate limiting
64c47856 DRF 3.7.4 changed how you delegate to another view, so don't
7359ca4f Is this right? It fixes two tests
fdd66e53 Adjust the expected error message for DRF 3.7.7
9257f68f The default TIME_ZONE should be UTC

(cherry picked from commit de8e158c)

* Install drf-yasg

* Add drf-yasg settings and urls

* Pin drf to make drf-yasg work

* Adjust config-models version to be compatible

* Remove django-rest-swagger (the old way)