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
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.