Add UTM cookie tracking for registrations.
Add config model for cookie names.

ECOM-5539

Use a contextmanager to cleanup after manipulating the current request in create_account tests for external auth

ECOM-4325

ECOM-1956

* Add a new cookie for user information
* Make marketing cookie names configurable.
* Handle URL reversal when URLs don't exist (in Studio)
* Move cookie code from student/helpers.py into its own module.

Also, I replaced a number of tearDown methods with addCleanup instead.
And also remove some unneeded patch.stopall() calls.

TNL-1493

See https://openedx.atlassian.net/wiki/display/TNL/User+API for details

These tests cover validation of parameters and saving of data to
UserProfile objects.

Add ENABLE_DISCUSSION_EMAIL_DIGEST feature, to enable discussion emails digest by default for all users

TNL-649

Disable sending activation email also when doing external_auth and setting BYPASS_ACTIVATION_EMAIL_FOR_EXTAUTH=True

Also improves handling in cases where account creation did succeed, but
comments service user creation did not.

Depends on commit 88abdd8a0b20bc9816f487b25abdea1953f5661d in https://github.com/edx/cs_comments_service

JIRA: FOR-522

This is necessary to allow non-browser-based services (e.g. notifier)
to know a user's preferred language even if the user has not explicitly
selected one.