Fully support nested Table of Contents

Right now BookFusion has partial supported for when a book has a Table of Contents that uses the nested format, so it displays a large complex hierarchy as seen below. This looks nice while viewing the TOC, but you cannot collapse them individually or all at once, and with a large TOC like in this book, it makes scrolling to find a chapter a little cumbersome.

Alternatively, when viewing the same book in Calibre which has full support for this formatting, you can see that the TOC can be collapsed, and each section expanded as needed. This allows for quick navigation, and an easier quick glance at how the book is organized.

For the reading experience, the normal ideal format would have the section the reader is in be expaneded, and all others automatically collapsed.

For example, if the reader was in Book Three, chapter 4, when they view the TOC it'd show Book One, Book Two, and everything from Book Four on as collapsed, but book Three would be expanded to show all the chapters within.