Update xblock-mentoring.

Update reference to the xblock-mentoring repository.

A bug where answers containing the string "??" would get mangled by jQuery has been fixed in xblock-mentoring.
update bok choy db caches
allow rsyslog to be none
updating handlers list to conditionally include syslogger-remote
Fix filter with new opaque key, allowing user to set COURSE_LISTING as old way path
update export_all_courses management command to count and list all failed export courses
Fix Video Player Initialisation Issue
Merge pull request #4691 from edx/ammar/fix-video-init-issue

Fix Video Player Initialization Issue
Allow verified to be offered without audit
fixup! Allow verified to be offered without audit
Add the ability to override non-standard verified mode names
Add an optional description field to course modes.
Fix up tests and enrollment behavior.
removing rake and  outdated references to it
Course Instructor as financeadmin role, will be able to download all purchase transactions in the course as a CSV file
Move a few HTML elements on the instructor dashboard page
updated the course registration models
added registration-codes generation functionality

rebased and resolve conficts with cdoge/registration_codes

feature enhancement request: added transaction group name text field to the download buttons as an extra optional query paramerter
added django admin pages for Coupon Table

added the suggested changes by cdonge
registration code checkout flow

Redirecting to dashboard after free user enrollment.