The EPUB ToC is now on par with the PDF ToC.

Change-Id: Iea714fdb68c825aa14345037e909c354bbd7cf00
Reviewed-on: https://gerrit.libreoffice.org/48346Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>