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)
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()
Add some optional policies around password resets, such as password reuse, forced password resets, allowed frequency of password resets
password history: just limit the result set range to simplify iteration logic
Update translations (autogenerated message)
Merge pull request #3115 from edx/sarina/update-i18n-translators-docs

Update Translation documentation
Added note about pages being publicly viewable

STUD-1488
Documentation for answer distributions
Merge pull request #2830 from edx/ahodges/documentation/answerdist

Ahodges/documentation/answerdist
Add multiple transcripts editor.

Fix donwload subs for non youtube videos and non-en language - continue.
Add acceptance tests.
Add detetion of assets on request.
Updated docstring.
Add fixes and acceptance tests.
Fix acceptance tests.
Update docsrtings and cleanup code, resful for language_id.
Specify exception type in POST.
Fix url in upload module.
Improve exception handling.
Remove 'en' and catching in editable_metadata.
Move descriptor.get_context test to lms tests.
Add query parameter to translation dispatch.
Response to format parameter of translatin GET request.
Fix Acceprance test: Metadata Editor.
move handlers to proper scores.
Split video player into smaller files.
Add ugettext and fix typoes.
Add changelog.
Support for downloading non-ascii filenames.
Change event binding.
Add content-language to download requests.
Reractor POST handler to not update self.transcripts.
Merge pull request #2899 from edx/alex/multiple_transcripts_editor

Alex/multiple transcripts editor
Upgrade JSdraw input.
Transcript translations should be displayed in their source language.
Fix tests.
Revert "Fix tests."

This reverts commit 1ed167d90a99c8f5d5884c9300a69ca5a7cc1d92.
Revert "Transcript translations should be displayed in their source language."

This reverts commit b4ba04bae9e3d44be92e6f870be5b80e9f464878.
Merge pull request #3088 from fmyzjs/patch-3

Update course_about.html