Book and Chapter Pages are Slow
When viewing a Book's TOC or any of its chapters, the entire chapter-list is loaded for the highest level book in the hierarchy, even if only a subset is needed. Depending on the size of the entire book, this can be a rather large query, and the way the chapter order for nested books is determined is somewhat inefficient.
Since we already have to create a dedicated book table for subscriptions, it's even more practical than before to include pre-generated parentlists and childlists. May be able to eliminate top_bookid once we make this change.
Also adding a previd and nextid to the chapter table could make the previous/next links much faster to generate.