Issue: Deleting Chapters Halfway

When using a Book's Edit tab to Delete Selected Chapters, the chapters are removed from the Book, but the article doesn't know that. That is, it's removed from the Book's Table of Contents, but if you visit the former chapter's Book tab, it's still under that Book.

Further, if we attempt to re-add the article to that Book, clicking 'Update Chapter' isn't enough. We must first save it to 'None', then re-add the chapter.

Fixed for the next build.