LMS-11237

Putting the new edx header behind a feature flag.

LMS-11228

LMS-11240

LMS-11235

LMS-11233

updating the version for django_countries

Clean up shopping cart processor API.
Fix UUID JSON serialization bug in CyberSource2 implementation.
Update test suite to use new CyberSource2 implementation.
Fix i18n messages in CyberSource2
Enable CyberSource2 implementation by default.

LMS-11217

Reuse the style from login and register views.
Remove all the specific style.

Remove duplicated code and make sure those views use the same visual
identity.

FOR-581

(The div with id "view-extensions" conflicts with the tab JS which sets location.hash to "view-x" in order to track the current tab)

LMS-11181

This commit adds a message to the instructor dashboard that is displayed when
no instructor tasks are currently running. This message is displayed where the
instructor pending tasks table would normally be placed, and is replaced
with the table when there are running tasks.

[STUD-2903]

Add session middleware to an external auth test to fix a test failure with the auto-registration AB-test changes

This addresses a bug in the email content history table where
"Unknown" was displayed in the number of emails sent column if any sort of
failure occurred during email sending. This behavior has been editted so now
the number of emails that failed to send is displayed, along with the number
of emails that were successfully sent. If the email task is still pending,
"0 sent" is displayed.

As a small addition, the table now also includes the authors of previously
sent emails, and the modal window for an email also displays its author.