CMS i18n changes from Tsinghua

Add an API to interact with users and preferences

Set to old xml defaults IFF no specified policy for problem nor course.

The new API uses Django REST Framework. For now, it is designed specifically
to support the use cases required by the forum digest notifier (not yet built),
with a goal of making it more generally useful over time.

Change delete asset prompt to Warning type for consistency.

Make release email script wiki-friendly

Allow session backend to be configurable 

Next gen modulestore

to cms settings (it was throwing 500s for Stanford when the CMS
calls render_from_lms)

Will/fix acceptance tests

Renzo/in context progress

Fix/foldit leaderboard

set django-wiki to its most recent version

Simple port of Class2Go's chat feature

A new modulestore backed by mongo that changes the data format to
facilitate easy versioning, sharing content between courses, and fast
lookup of course structure and Scope.settings data.

Conflicts:
	cms/djangoapps/contentstore/tests/test_contentstore.py

POST requests were claiming request.method == 'PUT'

Fix/vik/studio oe

Ned/studentmodulehistory cleaner command

So, changed handlers to look for either value.

Bug report: remove <?xml version..> tag

Fixes code_jail imports and draganddrop yaml

I18N work seems to have lost a very prominent space in the landing page

add a new django-admin command to dump out a course structure document. ...

https://edx-wiki.atlassian.net/browse/STUD-428