This is primarily so that we can manually fail zombie instructor
tasks that are clogging up the queue for a course.

We would like to be able to generate arbitrary reports and expose them to the instructor by simply uploading them to S3.  The existing grade download infrastructure pretty much supported that already, however, all of the internal and external structures were referring to the reports as exclusively grading related.

Fixes: AN-590

with code to translate between addressing schemes based on app
and persistence layer addressing scheme specification.

STUD-1206

When creating an instructor task total_num_items may change between the
time it and the number of subtasks is calculated and the time the
subtasks are actually queued (all of this cannot happen in one transaction).
In such a case the extra items are distributed among the subtasks of the
last query.

LMS-2090

LMS-1744

that are not present in a given student's gradeset.

General code cleanup and addition of comments.

Instructor dashboard API unit tests.

LMS-58

Hook up display of grade files ready for download to new instructor dashboard.

LMS-58

Adds xblock handler_url support to the LMS, and makes handle_ajax use
that code.

[LMS-230] [LMS-229]

Add cache-based locking to subtasks to ensure that the same task is not running in two workers at the same time.

Add cache-based locking to subtasks to ensure that the same task is not running in two workers at the same time.