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.
added course price set/view/edit functionality

added CoursmodeArchive model to save the old prices history

analytics -> instructor_analytics

analytics -> instructor_analytics
refund message for purchased courses

Add little more logic for paid courses
add more detail to new CourseModesArchive table
e-commerce UI suggested changes
Retrieving active coupon codes from model
Merge pull request #4254 from marcore/fix-branding-course-listing-opaque

Fix filter with new opaque key, allowing user to set COURSE_LISTING as o...
Annotations Tools: Fixing major Firefox/Tinymce bug in annotations

 - fixed issue in Firefox where the init gets called multiple times

 - fixed spacing issues and added more comments

 - fixed indentation, added missing parens in comment, and fixed typo
Merge pull request #4655 from edx/diana/allow-only-verified

Allow verified to be offered without audit
Update youtube api.
Merge pull request #4693 from edx/anton/fix-video-tests

Fix failing video tests due to wrong IFRAME_API_RESPONSE
Correct UnboundLocalError exception in student_migration_35
Text Annotation Tool: Safari Colored Highlights Bug Fix

 - fixed spacing
Merge pull request #4590 from edx/cdodge/fix-reg-codes

eCommerce enhancements (pt. 2)
Merge pull request #4675 from lduarte1991/lduarte-harvardx-pr14

Annotations Tools: Fixing major Firefox/Tinymce bug in annotations
Merge pull request #4518 from lduarte1991/lduarte-harvardx-pr13

Text Annotation Tool: Safari Colored Highlights Bug Fix
Replace `check_for_get_code` with `assert_request_status_code`

More flexible, uses the word "assert", method instead of function
BLD 1020: Easy access to Group Configurations page from Content Experiment component.