Any string can be used as delimiter between integer and fraction.
It is now saved/loaded to/from ODF, as it was from XLS.

Change-Id: Ie6364d1cdefc020ea615c18099118135c619f96b
Reviewed-on: https://gerrit.libreoffice.org/27262Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>