And simplify the code in sd/headerfooterdlg, no
need for the complex encoding of date and time when we
can just index into a static array.

Change-Id: I677400bf1f956c81eba665b71dbda9183b63f55c
Reviewed-on: https://gerrit.libreoffice.org/42346Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>