fdo#71883 Startcenter: Re-introduce the 'Tools' -> 'Customize...' menu

Change-Id: I4d3993dc855c030f8c51fe2ce3d364240e241dff
(cherry picked from commit 43d355d25db1144668a59346b37b041b8a9fdbc3)
Reviewed-on: https://gerrit.libreoffice.org/7333
Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>
(cherry picked from commit b24351e5e3565bbd2b8b724d83f4b4c1e0b9f8dc)
Reviewed-on: https://gerrit.libreoffice.org/7354
Reviewed-by: Eike Rathke <erack@redhat.com>
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>