Default is split on heading, but this allows e.g. split on page break
instead.

Change-Id: Ie392fc76f91d60029c7e5f2a0adc55cb18f6157d
Reviewed-on: https://gerrit.libreoffice.org/41577Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>