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

Depends on cs_comments_serivce commit ea218a2b038b59e63fd6593b5598db90223636e1.

TNL-543

TNL-172: Change type of a previously posted post. IMPORTANT: this commit depends on commit 774887b in cs_comments_service.

Fixes TNL-160

Also change server to pass post type through to the comments service.

Co-authored-by: jsa <jsa@edx.org>

Co-authored-by: Brian Talbot <btalbot@edx.org>

JIRA: FOR-591

Instead of allowing the JSONDecodeError to escape, raise an error
indicating the request id and containing the first 100 characters
of the response to aid investigation.

For now, this only includes course id, search terms, and result count.
Information is logged both to the standard logger for near-term analysis
and the event tracker for the longer term. Result count logging requires
commit 02466b1 of cs_comments_service (otherwise it will be null).

Previously, an error was raised if the comments service returned data
including an unexpected field, which unnecessarily complicated the
release path for new features, since the list of allowed fields would
need to be modified before cs_comments_service could be modified, and
only then could edx-platform take advantage of the new CS feature. We
still log a warning if an unexpected field is returned, so we will
still be able to tell if the CS returns a corrupt response.

JIRA: FOR-180

This commit adds the non-courseware lms/djangoapps and lms/lib.

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]

This requires cs_comments_service commit 1d50176.

This captures real-time metrics for all of the comment client actions,
segregated by course_id, as well as other small-cardinality fields.

The goal is to be able to detect changes in forum usage, with the goal
of alerting on potential error conditions.

Also improves handling in cases where account creation did succeed, but
comments service user creation did not.

Depends on commit 88abdd8a0b20bc9816f487b25abdea1953f5661d in https://github.com/edx/cs_comments_service

JIRA: FOR-522

JIRA: FOR-374

The relevant parameters and data are merely passed through between the
front end and comments service.

JIRA: FOR-374

This change requires cs_comments_service version 31ef160 or later. Now
that the /threads endpoint can filter by commentable_ids, use that
instead of the /search/threads endpoint, which does not sort and
paginate correctly.

Bug: FOR-224

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.

Logging the duration of each request will allow us to determine
whether there is a significant difference in the latency reported by
the comments service and that observed by the LMS. Each request will
be assigned a unique identifier to allow correlation of the reported
latency on each end.