First-level TOC should be automatically expanded

[lcawl]

Currently, the landing pages for our books have the full table of contents with only the top level pages visible. For example:

There is a content reorganization underway in several books which involves reducing the number of items at the top level of the navigation. Would it be possible to have a setting that expands the first level by default? For example, to show this level of information for each part:

Ideally this would be an option that could be set differently for each book (enabled/disabled).

[nik9000]

I talked to @lcawl and @gchaps and it looks like we'd like to be able to pick which sections we expand. If we can't pick then we'd just like to expand them all. But only in books that want it.