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.
Switch from Rake to Paver
Change `if not args.skip_collect` to `if args.collect`

Simpler and clearer
from __future__ import print_function

and print errors and warnings to sys.stderr
write_stderr() function is unnecessary
Pull Paver requirements out into a separate file
Insert *right* at the front
Changed str->unicode in common/djangoapps/utils/.

LMS-2436
Submission history view not internationalized.
LMS-2167
BLD-951: Fix flaky tests.
Merge pull request #3033 from edx/anton/fix-flaky-video-acceptance-tests

Video: Fix flaky acceptance tests.
Removing ipython from edx dependencies.

Ipython is not strictly required to run edx-platform. It can
be setup as part of Vagrant provision scripts, or manually
by each developer as required in specific cases.
Merge pull request #2938 from edx/waheed/lms2167-show-submission-history-not-internationalized

Internationalized submission history view.
Some more str->unicode fixes in instructor and courseware apps.

LMS-2429
Merge pull request #3047 from edx/valera/add_ipdb_requiement

Removing ipython from edx dependencies
i18n: make emails in lms translatable

The email texts in lms/templates/emails are not extracted by rake i18n:generate because the babel_mako.cfg does not include them.
And a several emails are not translatable because they do not use ugettext.
Revert to older version of TinyMCE.

We had trouble with Cloudfront/hashed files and need more time
to investigate.
This reverts commit e8f53ac9dc6d8a1d9928787635c7c5f7e409a9ec.
Merge pull request #3048 from louyihua/master

Make emails in lms translatable
Documentation for static page changes

STUD-1347