secure-cookies: Allow to use secure HTTPS cookies (Django setting)

Cf https://docs.djangoproject.com/en/1.4/ref/settings/#std:setting-SESSION_COOKIE_SECURE
Make code more robust to bad input (for case where DB was populated with string None)
Increase randomness of course name in testcase
Fix BulkAssertionMixin so that it actually asserts the truth/falsity of the contained assertions
Bump version of PyContracts so that it will disable the 'check' function
Teach mongo_connection to retry read operations in the face of AutoReconnect errors
Allow Timedelta and RelativeTime fields to handle from_json being passed timedelta objects
Make xml exports more comparable by sorting and indenting json
Export xml from the destination store during cross-modulestore import/export tests
Make Studio CoursePage objects generate the correct CourseLocator based on whether the DEFAULT_STORE is set or not
Inherit from JSONField rather than Field for json-based fields
update discussion blackout setting warning (TNL-442)
update password reset template (TNL-503)
Enable analytics dashboard link in instructor dashboard.
Update copy for link to analytics dashboard.
Merge pull request #5428 from rocha/enable-insights-link

Enable analytics dashboard link in instructor dashboard.
Use InheritanceMixin in more modulestore tests
Switch inheritance in split-mongo over to using InheritingFieldData.
Turn on bulk operations for xml export
Upgrade to a more performant version of opaque-keys