@jzoldak showed me that setting `USE_I18N = DEBUG` didn't actually accomplish
what I had hoped it would -- changing DEBUG didn't also change USE_I18N.
This pull request accomplishes what I was trying to accomplish, without being
quite so clever about it.

Add AUTOMATIC_VERIFY_STUDENT_IDENTITY_FOR_TESTING flag so that acceptance tests can run through certificate identity verification flow.

Adds a new Email link to the instructor dashboard for frontend interface to send
email to course members. Adds a feature flag ENABLE_INSTRUCTOR_EMAIL to toggle this.
Creates a new djangoapp bulk_email that handles this action by getting the recipient
list and batching the emails to different celery tasks to do the actual sending.
Requires lynx package to convert HTML email to plaintext. Handles SMTP errors by
retrying or falling through to the next email. Adds the option to opt out of course
specific emails in the user dashboard with an Email Settings link for each course.
Uses severable configurable settings with defaults. DEFAULT_BULK_FROM_EMAIL
specifies the from address for email. EMAILS_PER_TASK specifies the number of emails
each celery task takes on. EMAIL_HOST, EMAIL_PORT, EMAIL_HOST_USER,
EMAIL_HOST_PASSWORD, and EMAIL_USE_TLS for the SMTP email backend settings.

Co-authored-by: Akshay Jagadeesh <akjags@gmail.com>

when in a dev environment.

when in a dev environment.

not common.  This ensures that we load the MITX_FEATURES
token BEFORE deciding to disable CSRF.

This is achieved by allowing access if settings.DEBUG is True and
settings.EDX_API_KEY is not set or None (which is true for dev.py)

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.

Expanded tests of hint_manager.

Enabled the hint_manager by default in development environments.

Expanded tests of hint_manager.

Enabled the hint_manager by default in development environments.

Highlights:
* The url '/shib-login/' interfaces with apache/mod_shib via
  request.META to handle shibboleth login and registrations
* Courses can designate 'enrollment_domains' to limit enrollment
  to users with a linked ExternalAuthMap verified by a particular
  identity provider
* Tests
* Logging

 Changes to be committed:

	new file:   common/djangoapps/external_auth/migrations/0001_initial.py
	new file:   common/djangoapps/external_auth/migrations/__init__.py
	new file:   common/djangoapps/external_auth/tests/test_shib.py
	modified:   common/djangoapps/external_auth/views.py
	modified:   common/djangoapps/student/views.py
	modified:   common/lib/xmodule/xmodule/course_module.py
	modified:   lms/djangoapps/courseware/access.py
	modified:   lms/djangoapps/courseware/tests/test_access.py
	modified:   lms/envs/common.py
	modified:   lms/envs/dev.py
	modified:   lms/envs/test.py
	modified:   lms/templates/courseware/course_about.html
	modified:   lms/templates/dashboard.html
	modified:   lms/templates/extauth_failure.html
	modified:   lms/templates/navigation.html
	modified:   lms/templates/register.html
	modified:   lms/templates/signup_modal.html
	modified:   lms/urls.py
	renamed:    lms/wsgi_apache.py -> lms/wsgi_apache_lms.py

Tell segment IO whenever a page is loaded.  Once this works, we
can add more detailed instrumentation for events we care about.

Will be turned off in prod until the SEGMENT_IO_LMS feature flag is
set to True and a SEGMENT_IO_LMS_KEY is set.

Developers can have private settings files by creating
lms/envs/private.py or cms/envs/private.py.  They are imported
at the end of dev.py.  Note that they won't be imported if you
are using one of the other dev*.py variants.

Start linting envs files, add task to only pylint errors, and move pylintrc file to the correct location

* hide the login behind a setting that is turned off by default
* clean out some of the outdated settings and hardcoded test strings

Change the parameters of the sass compiler to output source
maps. Google Chrome uses the maps in the debugger to show the sass or
scss file that originated the style for a particular element.

More information here:

http://fonicmonkey.net/2013/03/25/native-sass-scss-source-map-support-in-chrome-and-rails/

move the instantiation of the metadata cache out of modulestore.py as it was causing a circular import dependency when running on AWS. Put instantiation into one_time_startup.py which I believe is run before any Django requests are handled