EDUCATOR-229

EDUCATOR-11

This specifically enables/disables the underlying comment service client
used to make calls to the service.  When disabled, this client will now
throw an exception which can be propagated upwards so that callers can
make the right decision about how to notify users of the error, or
handle retry, etc etc.

Discussion is restricted to the CCX course (there is no sharing of
discussions with the parent course or other CCX instances).

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.

These signals are caught by the Teams app and used to update
`last_activity_at` on both teams and individual users.

TNL-2497

Caches all permissions per user per course. Adds caching functionality to has_permission and replaces all instances of cached_has_permission with has_permission.

Also, I replaced a number of tearDown methods with addCleanup instead.
And also remove some unneeded patch.stopall() calls.

between brackets

between brackets

[LMS-2757]

This commit updates common/djangoapps.

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]

STUD-1140

JIRA: FOR-398, FOR-399

This applies to global staff (is_staff=True), not course staff.
Previously, staff were granted the Moderator role but not the Student
role upon enrolling in a course. If the Moderator role were later
revoked, then the user would have no role and be unable to post in the
forums, which is confusing for the user. edX staff indicated they would
prefer to not automatically receive the Moderator role, so the Student
role is granted instead. Note that staff will still be able to grant
themselves Moderator privileges through the instructor dashboard if
they wish.

JIRA: FOR-338

switch to using get() rather than get_or_create(). Also add a test case with a different casing on the courseId

define a unseeding forums permissions and call into it from delete_course

define a unseeding forums permissions and call into it from delete_course

Features coming down the pipe will want to be able to:
* Refer to enrollments before they are actually activated (approval step).
* See what courses a user used to be enrolled in for when they re-enroll in
  the same course, or a different run of that course.
* Have different "modes" of enrolling in a course, representing things like
  honor certificate enrollment, auditing (no certs), etc.

This change adds an is_active flag and mode (with default being "honor").
The commit is only as large as it is because many parts of the codebase were
manipulating enrollments by adding and removing CourseEnrollment objects
directly. It was necessary to create classmethods on CourseEnrollment to
encapsulate this functionality and then port everything over to using them.

The migration to add columns has been tested on a prod replica, and seems to be
fine for running on a live system with single digit millions of rows of
enrollments.

add a migrations to the new django_comment_common to keep things a bit more consistent with our normal useage.

update comment models.py to not have the dependency on get_course_by_id (which is in LMS). Also explicitly set the db_table name because django auto generates table prefixes according to the djangoapp name

move some files from lms/djangoapps/django_comment_client to common/djangoapps/django_comment_common