This reverts commit 74bc970e.

This reverts commit a1c01882.

AA-152: Course Start Date for PLS

Fixed lint issues

PROD-1609
PROD-1610
PROD-1614
PROD-1615
PROD-1616

PROD-1506

Code Refactor

PROD-1602

Updated the displayed start date for a learner in a self paced course
that appears in the Learner Dashboard and the Dates tab.
Used the max of the course start date and the learner's enrollment date.

Fixed Import error due to pre tag

* remove old_format reference in teams config

* validate uploaded character values for team csv upload

Co-authored-by: Ben Warzeski <benwarzeski@edX-C02CD0HCLVDM.cable.rcn.com>

AA-164: Performance fixes for course home

* remove old_format from team config tests

* remove old format from teams_config

Co-authored-by: Ben Warzeski <benwarzeski@edX-C02CD0HCLVDM.cable.rcn.com>

This reverts commit 1d7ff32a.

Fixed regex for nested pre tags

Updated import export test

fixed quality test issue

fixed No exception type(s) specified

updated tests

fixed linter issue

fixed linter issue

fixed linter issue

* Commits:
  Add is_staff check to masquerade POST
  Convert masquerade view to class-based

[CRI-174] [BB-2402] Fix LTI issues due to duplicated Content-Length header

AA-115: Adding external API for dates tab

This adds in the API for the Dates Tab for use by the
Course Home MFE.

Cleaned up a few more things about the testing configuration now that we've deployed Django 2.2 to production:

* Go back to a single version of django-oauth-toolkit, tox doesn't need to vary it anymore
* Go back to PyPI release of django-method-override
* Remove no longer needed dependency on python-oauth2 (we already removed the package it was used by)
* Update prepare_xdist_nodes.sh with new Django requirements file options

Remove code from the courseware index page that was only relevant if the shopping cart was enabled.

Restrict api to staff users