Variable decimal is only saved in ODF for number, and do not consider
partial variable decimal: 0.0## is saved as 0.000
This patch extend ODF with loext:min-decimal-digit for number format and
scientific format

Change-Id: I5022458da47bbd33c3e195c280e75c43faca5f8d
Reviewed-on: https://gerrit.libreoffice.org/15135Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>