updated pdf viewer
i18n: Fix the chinese name of chinese language

The current version of chinese language's chinese name is not political neutral.
In fact, which form of chinese (traditional or simplified) can be called "正體"(in traditional chinese) or "正体"(in simplified chinese) is not globally defined.
So, I change the name according to the word used by Microsoft Windows, which is more neutral.
Update course_about.html

if course title use Chinese or other language got the 500 error when visit the course_about page ,and the log shows :UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-3: ordinal not in range(128)
temporarily remove SR on capa alerts to fix problem submissions (LMS-2474)
Remove unused methods from comment_client
Remove unused *args and **kwargs from perform_request
Use requests library utility method for getting json results
Add more tags to comment_client request metrics

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.
Merge pull request #3105 from edx/adam/hotifx-js

temporarily remove SR on capa alerts to fix problem submissions (LMS-247...
Add datadog metrics logging for django model creates, updates, and deletes
Merge remote-tracking branch 'origin/release' into adam/merge-release-2
Merge pull request #3113 from edx/adam/merge-release-2

Adam/merge release 2
Custom JavaScript Display and Grading

DOC-105
Merge pull request #3006 from edx/markhoeber/documentation/DOC-105

Markhoeber/documentation/doc 105
Disable failing video test
Merge pull request #3114 from edx/zoldak/skip-failing-video-test

Disable failing video test
Merge pull request #3061 from cpennington/model-metrics

Add datadog metrics logging for django model creates, updates, and deletes
Merge pull request #3062 from cpennington/comment-client-metrics

Add metrics to comment_client requests
Update Translation documentation
Update reference to the xblock-mentoring repo for optimized dataexport

The new ref is gsehub/xblock-mentoring@43aa320

Optimize mentoring-dataexport times by using values_list()