Prepare for "Japan's Y2K" Gengou calendar era switch after 2019-04-30

The emperor Akihito will abdicate on 2019-04-30. The next emperor
will be Naruhito, but so far neither the new era name (Heisei for
Akihito) nor its abbreviation or a Unicode character are
determined. At least introduce the new era with some dummy names
(Naruhito,Na,N).

Change-Id: I8c0af390ca0408ac259e47e7eaf2e49b5889c9ba
Reviewed-on: https://gerrit.libreoffice.org/58142Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins

Introduce next Japanese gengou era 'Reiwa'

starting from 2019-05-01, which has been announced officially.

This fills the provisional slot acknowledged at
cacbb0fa.

Change-Id: Ifb12e6afaad4c66d455f664b46ec946e80324e87
Reviewed-on: https://gerrit.libreoffice.org/70157Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins
Reviewed-on: https://gerrit.libreoffice.org/70185