LEARNER-1696

TNL-6050

instead of using the base course key (which does not contain the CCX info).
This removes the need for special checking of CCXKey/CCXLocator types, and just
treats them like normal CourseKeys.

This fix allows users with a Staff role on a CCX course to view CCX courses in Insights.

* Centralize creation of quick request objects.
* Isolate caches to individual tests to prevent test ordering
  dependencies.

TNL-5811

TNL-5046

Previously, the mobile api did not check for pre-requisite courses
or entrance exams. This change checks for these milestones and then
returns course content accordingly.

LoginEnrollmentTestCase.setup_user: Attribute 'user' defined outside __init__

for visual indent

LMS-11189

More flexible, uses the word "assert", method instead of function

This commit updates lms/djangoapps/courseware.

These keys are now objects with a limited interface, and the particular
internal representation is managed by the data storage layer (the
modulestore).

For the LMS, there should be no outward-facing changes to the system.
The keys are, for now, a change to internal representation only. For
Studio, the new serialized form of the keys is used in urls, to allow
for further migration in the future.

Co-Author: Andy Armstrong <andya@edx.org>
Co-Author: Christina Roberts <christina@edx.org>
Co-Author: David Baumgold <db@edx.org>
Co-Author: Diana Huang <dkh@edx.org>
Co-Author: Don Mitchell <dmitchell@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Nimisha Asthagiri <nasthagiri@edx.org>
Co-Author: Sarina Canelake <sarina@edx.org>

[LMS-2370]

LMS-1192

In the middle of addressing pull request comments. This is a safety commit in case I have to revert some changes I'm about to make.