add parameter to supress dialog

With the new parameter you can now supress the dialog for document
compare in writer.

Change-Id: I984ee75552e5c006332331510df5d437b687903f
Reviewed-on: https://gerrit.libreoffice.org/8739
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>