Add missing title to the Header and Footer dialog

Change-Id: I720bf1be02b9b4decf5373d49de136b0e57c61c9
Reviewed-on: https://gerrit.libreoffice.org/11657
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>