Add task-history-per-student button, and fix display of task messages.

column from task-in-progress table).

Add unit tests for regrading at courseware level (task and task_queue).

CourseTaskLog fully after task submission, so it works in Eager mode
(for testing).

Refactor tracking and xqueue initialization to no longer require a request.  Get tracking logs to work.  Add transaction annotations.

Make sure to read only once from result objects when getting result status,
so that values are consistent.

from client.  Tasks.py remains the task implementations running on the
celery worker.

In particular, move status message generation out of task thread to client side.

Add call to MakoMiddleware() to initialize templates in celery worker server.

Pass task_ids by POST properties (as a list) to collect task progress status.

Add CourseTaskLog, and make calls to regrading.

Add regrading implementation, and hack the marshalling of request.

Jonahstanley/add navigation tests

Anton/videoalpha tests

Fix for broken forums due to forum entry with no start_date

Switch to using environment variables to get key for Segment.io

Bug fix for LaTeX source not saving

CHANGELOG entry for the whitelistable sandboxing change.

need to comment out another thumbnail check due to build test environmen...

need to comment out another thumbnail check due to build test environment not having libjpeg installed

These CHANGELOGS were never used, and are now obsolete.

css_click will try clicking multiple times.

disable assertions on thumbnail generation as it puts a system requireme...