CLC-2425 Instructor section nesting by Course Option

https://jira.media.berkeley.edu/jira/browse/CLC-2425
https://jira.media.berkeley.edu/jira/browse/CLC-2426

At UC Berkeley, many secondary sections are not explicitly assigned an instructor in campus data. Instead, the instructor is determined implicitly by a primary section's instructor. Currently, CalCentral My Classes and My Academics, and bCourses Course Provisioning, do not match instructor expectations because they only include explicit instructor records. Also, as noted at CLC-2425, lack of implicit nesting means that bCourses course sites often aren't positioned correctly in My Classes.

This PR adds implicitly nested secondary sections to My Classes, My Academics, and Course Provisioning feeds.

This initial change does not try to handle implicit-instructors in a bottom-up way. For example, in the My Academics class page, the secondary sections do not display with a list of their (implicit) teachers. Making that work efficiently will be a tougher job and is a lower priority, and so I'd like to put it into a follow-up task.