make embargo template theme-able

Use "Stanford-style" theming to enable you to put your own embargo
notice up.
missing themed embargo page fails safely to unthemed
updated pdf viewer
Added ENABLE_MKTG_SITE to Features
Added myself to author file
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
Merge pull request #3032 from IONISx/feature-enable-mktg-site-is-missing

Added ENABLE_MKTG_SITE to Features
Display error page templates, for testing purposes

This commit allows us to test the server error template by visiting `/500`. This
way, we can catch errors in our error templates, instead of having infinitely
recursing errors.
Merge pull request #3060 from edx/db/display-error-pages

Display error page templates, for testing purposes
Fix Studio's XBlock dependency loading issues

STUD-1465

Changed the XBlock rendering logic to use promises to track asynchronous tasks.
Each dependency is then only loaded once the previous one has completed, and the
XBlock initialization only happens once all dependencies are loaded. This gives
XBlocks the same semantics in Studio as they get when shown directly on a page.
Merge pull request #3046 from edx/andya/fix-xblock-loading-in-studio

Fix Studio's XBlock dependency loading issues
Added template for iFrames. [BLD-611]
Merge pull request #3055 from edx/jmclaus/feature_iframe_template

Added template for iFrames. [BLD-611]