Issue #1945390 by Alan Evans, disasm, tim.plunkett, dawehner: Convert book_admin_edit() to a new-style FormInterface implementation.

Issue #1938316 by disasm, jaskho, stella, scor, tim.plunkett, jibran | Crell: Convert book_outline() to a new-style Controller.

Issue #1498674 by plach, das-peter, Schnitzel, dawehner, YesCT, attiks, Berdir, Gábor Hojtsy, Soul88, Carsten Müller: Refactor node properties to multilingual.

Issue #1938296 by disasm, YesCT: Convert book_admin_overview() and book_render() to a new-style Controller.