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
Update final text strings & readthedoc URL

TNL-401
Address PR review comments
Make student profile CSV download a background task, add cohort column
Merge pull request #5473 from edx/dan-f/background-student-profiles-add-cohort

Make student profile CSV download a background task, add cohort column
Merge pull request #5475 from edx/andya/cohort-doc-fixes

Update final text strings & readthedoc URL
Disable flaky JS FileUploader SystemFeedback and NotificationView tests
TNL-559
Fix error when doing non-ASCII forum search

Fixes TNL-160
Add cohort information to forum search events
Remove dead code
Add events for cohort modifications

This includes cohort creation/deletion and membership changes.
Merge pull request #5463 from edx/gprice/cohort-events-take2

Cohort events
Add documentation for cohort events
fixup! Add documentation for cohort events

Reword description of auto vs. manual creation of cohorts and user
addition to cohorts.
Make notifier API resilient to bad enrollments

Previously, the user endpoint would would return 404 for any request
involving a user having an enrollment for a course that no longer
existed.
Create Donation order item
Add tax-deductible messaging to the confirmation email and receipt pages.
Update receipt page to make the course URL optional
fixup! Make notifier API resilient to bad enrollments

Add explicit course key to enrollment for non-existent course in test case
Merge pull request #5489 from edx/gprice/notifier-api-bogus-enrollment

Make notifier API resilient to bad enrollments
Merge pull request #5488 from edx/gprice/cohort-events-doc

Add documentation for cohort events
TNL-549: Fix thread editing.