Add a new waffle switch that allows us to assume zero grades for
learners who have no entry previously recorded, and another to
disable persisting grades for unengaged learners.

TNL-6691

TNL-6674

Remove deprecated SingleSectionGrader.  TNL-5987
Remove display_name and module_id from Scores objects
Update CourseGradeFactory.__init__ to not be user-specific
Update some callers to use CourseGrade class instead of "summary" dict
Remove no longer needed course_grades.py module.
Renamed django signal from GRADES_UPDATED to COURSE_GRADE_CHANGED

For TNL-5993

Ability to create two or more LTI consumers through the Django admin with an empty instance_guid field.

TNL-5778

Makes use of the new SUBSECTION_SCORE_CHANGED signal to trigger a task that
updates persisted course grade values. We've also renamed SCORE_CHANGED to
PROBLEM_SCORE_CHANGED to head off any issues with unclear signal names.

TNL-5740

For better user-facing performance, the SCORE_CHANGED signal is now handled by
enqueueing an async task to update the relevant stored grade, rather than
making the request wait until that operation finishes.

TNL-5738

The "oauth_body_hash" appeared twice in the auth header in the request
when posting grade back to tool consumer. However, the signature sent
from edX is calculated based on only one oauth_body_hash.
On the tool consumer side, the signature is calculated based on the auth
header and will use the duplicated fields. So the signatures will not match.
And request will fail the signature validation.

The bug was introduced in this commit:
https://github.com/edx/edx-platform/commit/03cee389e0869263f5f9977098770495b5216733
on July 12th by updating the oauthlib.

Because 0.7.2(original version) doesn't have oauth_body_hash support, so a custom
OAuth1 client was implemented to add oauth_body_hash to the headers:
https://github.com/edx/edx-platform/blob/f5d0f3ff55d264ed4b68a24808b255aef5d8dad2/lms/djangoapps/lti_provider/outcomes.py#L24.
However, the new oauthlib 1.0.3 has support for oauth_body_hash
(https://github.com/idan/oauthlib/commit/51675237c410b413a11091926436420493c52866#diff-c2a1e5f1ddfe8e48ff62b59eb952644eR180).
So after updating library, oauth_body_hash is added twice.

This fixes the bug by removing the custom client and use the oauthlib
default client to generate the auth header.

* First take at forcing a subsection's grade to update when a signal is
  sent that a problem's score has changed
* Refactor signal handler connection.
* Expand bokchoy tests to cover progress page
* Add some grading unit tests

TNL-5394
TNL-5364

https://openedx.atlassian.net/browse/TNL-5008

More accurately, this creates a 4th shard because the
last shard is always the default.

More accurately, this creates a 4th shard because the
last shard is always the default.

The problems render properly in IE 10 & 11 when using edX directly, or when opening LTI in a new tab.
This is reproducible in Canvas and D2L

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

Also remove useless docstrings where they were added to keep pylint
quiet.

You can still edit this to meet your needs, but you won't need to
manually generate one.

This mimics the data displayed in our oauth2 client listing and allows
you to search on identifying fields.

This is necessary to properly implement the LTI outcome passback
spec. It was not included previously because it was causing problems
with Canvas, but Blackboard will not accept outcomes unless they are
properly signed.

The requests_oauthlib doesn't support the body hash spec out of the
box, so BodyHashClient needed to be made. Fortunately, it's a pretty
simple spec:

https://oauth.googlecode.com/svn/spec/ext/body_hash/1.0/oauth-bodyhash.html

The instructions say that this should be left blank until the
initial launch, but Django Admin kicks that out because blanks
are not allowed at the model level.

This change allows graded assignments to be added to a campus LMS
regardless of the granularity at which the problem sits. Previously
a grade could only be returned if the usage ID for the problem itself
was specified in the LTI launch.

The code assumes that courses taking advantage of this functionality
are arranged in a hiearchy (with sections being parents to verticals,
and verticals being parents to problems). When a grading event occurs
it traverses the parent hiearchy to identify any previous graded LTI
launches for which the new scoring event should generate a grade
update. It then calculates and sends scores to each of those outcome
services.

Since grade calculation is an expensive operation, the code optimizes
the case where a problem has been added only once as a leaf unit. In
that case it is able to behave as before, just taking the grade from
the signal without having to calculate grades for the whole course.