Studio: adds a space back to the phrase 'Welcome to edX Studio'

Correctly persist checklist settings.

Incidentally, fixes an acceptance test (which would have caught this
bug) not running. Its step regex was "They are correctly selected
after I reload the page$", which happens to be matched by "I reload
the page$", another step definition. Lettuce seems to arbitrarily pick
between definitions if they both match a step, so it's good to ensure
that each step isn't a sub-regexes of another.

Add endpoints to set user notification preference

Fixes for `vagrant up`

Two endpoints are intended to be used by AJAX calls from the web UI with an
authenticated user. When enabled, the value of the preference is an encryption
of the username, to be used as a token for one-click unsubscribe links. The
third endpoint is the target of unsubscribe links, which displays a page with
an appropriate message to the user.

Validate date/time settings when typed in directly.

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 

vagrant:
  - check actual IP;
  - only init machine first time, just as native installations;
  - add .bash_profile to permissions fixup;
  - cleanup excessive newlines in making .bash_profile;

README:
  - include admin & debugging use;
  - info about re-initializing VM & manually running create-dev-env.sh;
  - add django admin & debug_toolbar setting info

Conflicts:
	AUTHORS
	scripts/vagrant-provisioning.sh

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