Upgrade Django to 1.11.12

Bump bok-choy to v0.7.2

Add some common functionality for retiring users

Fixed error: ImportError: No module named notmigrations

LEARNER-4403: Update TOS and Privacy Policy field on registration form for GDPR.

- Methods for getting hashed retired users and usernames
- A DRF permission for retiring users

Reverting celery task kwarg name.

Account for Django block on DDL in transactions

Remove deprecated make_option from certificates management commands

fix REV-19 experiment check for refunds

Aj/learner 4493

allow site and mode to be nullable in admin form

Protection for when there is no CourseOverview data available.

reorder 0017_auto_20180327_1631 to be after the other 0017

The migration 0017_remove_icon_class_image_secondary_fields was in
conflict with 0017_auto_20180327_1631, so we bump the latter to 0018.

Merge release back to master

issues

[LEARNER-4493]

Add chapter index to dom

Route sailthru tasks to lms ace queue instead of default.

Ibrahimahmed443/wl 1491

Show inline discussions by default

LEARNER-4801

Logging: Error getting the course from modulestore

Use get or create rather than create

Link to LMS from Studio footer