Adds a waffle switch edx_proctoring.rpnowv4_flow which gates several
learner workflow changes which will need to be applied at the time we
cut over a platform to using RPNow version 4 rather than version 2.

JIRA:EDUCATOR-3765

This adds a new django app -- edx-when -- that will copy start and due dates to mysql and allow per-learner overrides in the instructor dashboard, using the existing IDDE interface.
It adds a data migration for existing IDDE data.

JIRA:EDUCATOR-4242

The pinned version is the one tagged with a release that is also on
PyPI.

https://github.com/jazzband/django-pipeline/tree/1.5.3

Use PyPI instead since that will be faster.

This has the effect of preventing Open edX installations from having
details which should be in configuration (because they're
edx.org-specific) end up in their applications.

revert pillow version

was causing issues with PT exam configuration dashboard launch

This reverts commit 544c7f7e.

This is necessary to allow new proctoring backends to mark proctored
attempts in error, often due to unuploaded files from the application
or issues with multiple sets of files attached to the same testing
session.