The learning_sequences app has its own model for Course Outlines.
Prior to this commit, these course outlines were only populated by
a management command in the learning_sequences app that queried
modulestore. This commit does a few things:
1. Move the update_course_outline command to live in contentstore
(i.e. Studio). This makes learning_sequences unaware of
modulestore, and makes it easier for us to extract it from
edx-platform (or to plug in different kinds of course outlines).
2. Add tests.
3. Add performance and debug logging to course outline creation.
4. Make course outline creation happen every time a course publish
happens.
This will allow us to start collecting data about how long building
course outlines takes, and get error reporting around any content
edge cases that break the course outline code.
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