Updated acceptance tests to match new behavior in video captions.

Unanswered on input

Jbau/bulk email faster tests

Adam/calc refactor

Move mitxmako initialization to a startup module

Upgrade newrelic agent to the latest version

Kill processes after running rake

Instrument course email for DataDog

Small change to email registration template

Affects:
Choicegroups, option inputs, textline, and formula equation inputs

Rewriting of links for Course Updates and Course Handouts.

    Added some text to guide the student to register with a particular email address.
    This is the one that was entered into the enrollment/invitation form by the instructor.
    Modified the template and associated test.

Properly display student progress

Remove network calls in test suite

STUD-669.

Course email for instructors

Adds the edX Marketing-approved template as html default.

Includes Data + Schema migrations for optout email -> user.id change.
Note that migrations should be reversible.

Some minor pep8 cleanup

Switch to using decorators; refactor and cleanup tests.

 Delay for possible race condition with fetching course email object.
 Use settings.SITE_NAME for host name to generate email footer url.

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>