Studio: Revised CSS Architecture (resolves STUD-806)

Verified Certificate Upsell

Fix a couple pylint violations

Peer grading linking issue

Break out Advanced Problem tests into a Scenario Outline

LMS-1127

pylint: db is a valid variable name

LMS-1127

E0d/specify coffee sources

LMS-1127

LMS-1127

Disable problem editor test

Added a [code] block to the problem markdown parser

Remove the use of celery.group from bulk email subtasks.

Improve forums performance

Avoid recomputing course module information for every thread, which
should dramatically improve the performance of high-percentile latency
queries.

JIRA: FOR-250

The _DISCUSSIONINFO global was originally used as a cache, but has since
lost that capability and is therefore just harmful. This is a precursor
to more refactoring that will improve the performance of the forums and
may itself provide some performance improvement because it separates the
computation done by two functions that each previously computed the
entirety of _DISCUSSIONINFO.

Improved release script

Allow the export_course command to dump results to stdout

This is in preparation for significant refactoring of the code in
question.

Improve forum error handling

Add explicit wait to JS transcript tests

CommentClientError now has sane subclasses that are meaningfully
distinct, and each subclass is handled appropriately. Errors raised by
the requests library are no longer handled by turning them into
CommentClientErrors, since there is no meaningful handling we can do,
and this way we will get more visibility into why errors are occurring.
Also, HTTP status codes from the comments service indicating client
error are correctly passed through to the client.