This reverts commit f97f0525, reversing
changes made to 800bcd8e.

incoming scores.

TNL-6697

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-6227

TNL-5990

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

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

TNL-5046

TNL-5686

TNL-5465

ECOM-5081

Adds ENABLE_SUBSECTION_GRADES_SAVED feature flag to both lms and cms. Also
installs the wiring that will allow robust grades to be used for courses
that enable it. This functionality is still gated by the feature flag
and should not be used until the remaining robust grades work is finished.

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

Performance improvement, this cache is no longer needed thanks
to block_structure caching data.

TNL-4874

By default, disable all caching in tests, to preserve test independence.
In order to enable caching, inherit from CacheSetupMixin, and specify
which cache configuration is needed.

[EV-32]

This abstract class contains most of the fields (aside from the id and
foreign key to StudentModule that the subclasses need to manage).  It
also provides a get_history method that abstracts searching across
multiple backends.

Move router code to openedx/core
We need to use it from cms and lms.
Ensure aws_migrate can be used for migrating both the lms and cms.

Handle queries directed to student_module_history vs default and the
extra queries generated by Django 1.8 (SAVEPOINTS, etc).

Additionally, flag testing classes as multi_db so that Django will
flush the non-default database between unit tests.

Further decouple the foreignkey relation between csm and csmhe

When calling StudentModule().delete() Django will try to delete CSMHE
objects, but naively does so in the database, not by consulting the
database router.

Instead, we disable django cascading deletes and listen for post_delete
signals and clean up CSMHE by hand.

Add feature flags for CSMHE
One to turn it on/off so we can control the deploy.
The other will control whether or not we read from two database tables
or one when searching.

Update tests to explicitly use this get_history method rather than
looking directly into StudentModuleHistory or
StudentModuleHistoryExtended.

Inform lettuce to avoid the coursewarehistoryextended app

Otherwise it fails when it can't find features/ in that app.

Add Pg support, this is not tested automatically.

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.

Skipped 'print' statement violations, as print() is Py3k syntax.

The progress page did a number of things that make performance terrible for
courses with large numbers of problems, particularly if those problems are
customresponse CapaModule problems that need to be executed via codejail.

The grading code takes pains to not instantiate student state and execute the
problem code. If a student has answered the question, the max score is stored
in StudentModule. However, if the student hasn't attempted the question yet, we
have to run the problem code just to call .max_score() on it. This is necessary
in grade() if the student has answered other problems in the assignment (so we
can know what to divide by). This is always necessary to know in
progress_summary() because we list out every problem there. Code execution can
be especially slow if the problems need to invoke codejail.

To address this, we create a MaxScoresCache that will cache the max raw score
possible for every problem. We select the cache keys so that it will
automatically become invalidated when a new version of the course is published.

The fundamental assumption here is that a problem cannot have two different
max score values for two unscored students. A problem *can* score two students
differently such that they have different max scores. So Carlos can have 2/3 on
a problem, while Lyla gets 3/4. But if neither Carlos nor Lyla has ever
interacted with the problem (i.e. they're just seeing it on their progress
page), they must both see 0/4 -- it cannot be the case that Carlos sees 0/3 and
Lyla sees 0/4.

We used to load all student state into two separate FieldDataCache instances,
after which we do a bunch of individual queries for scored items. Part of this
split-up was done because of locking problems, but I think we might have gotten
overzealous with our manual transaction hammer.

In this commit, we consolidate all state access in grade() and progress()
to use one shared FieldDataCache. We also use a filter so that we only pull
back StudentModule state for things that might possibly affect the grade --
items that either have scores or have children.

Because some older XModules do work in their __init__() methods (like Video),
instantiating them takes time, particularly on large courses. This commit also
changes the code that fetches the grading_context to filter out children that
can't possibly affect the grade.

Finally, we introduce a ScoresClient that also tries to fetch score
information all at once, instead of in separate queries. Technically, we are
fetching this information redundantly, but that's because the state and score
interfaces are being teased apart as we move forward. Still, this only
amounts to one extra SQL query, and has very little impact on performance
overall.

Much thanks to @adampalay -- his hackathon work in #7168 formed the basis of
this.

https://openedx.atlassian.net/browse/CSM-17

* Remove m2m relation between credit course and credit providers.
* Separate eligibility and provider APIs into different modules.
* Add API call for retrieving a user's eligibilities.
* Cache credit course list.
* Style the dashboard purchase button.
* Display a link for the credit provider on the dashboard.
* Add analytics events for clicks on the purchase button.
* Expose more credit models to Django admin and add search functionality.

Displayed eligibility line items on the Progress page of a Credit course
in the order of appearance in the courseware.

ECOM-1782

force save "download_video" field if not set

set timezone to UTC explicitly