Just a dummy implementation so far. Needed because customer Automation
client software seems to access it (through the very obsolete
WordBasic API, even). It remains to be seen whether any actual mail
merge functionality is needed.

Change-Id: I40419da544f61173e4bcf759b887997c7f233b02
Reviewed-on: https://gerrit.libreoffice.org/55727Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tor Lillqvist <tml@collabora.com>