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>