– by adding and using narrow month names "jan."–"dec." (abbreviated
month names are still Roman numbers for back-compatibility);

– by adding ortographically incorrect, but "interoperable/back-compatible"
  typewriter & Excel format "YYYY.M.D.";

– by replacing one of the "YYYY. MMM. D." by "YYYY. MM. DD.".

Other changes:

– replacing incorrect "YYYY. M. D." format with the ortographically
  correct "YYYY. MM. DD." format. We keep its long YYYY format for
  back-compatibility. (This system format is visible only on the extra
  page of the Date formatting list, so it's not an annoying duplication.)

– abbreviated eras use non-breaking narrow spaces.

Note: there is also a not so annoying duplication, the "YYYY-MM-DD HH:MM:SS",
not on the first page of the date list in the dialog window and not in the
XML file, but only on the second page of the date list. For back-compatibility,
we keep this format in the XML file.

Change-Id: I4c49d637710295395b75034aa50015a5f3719d89
Reviewed-on: https://gerrit.libreoffice.org/59171
Tested-by: Jenkins
Reviewed-by: László Németh <nemeth@numbertext.org>