ODF1.3 implement a new attribute for engineering notation
https://issues.oasis-open.org/browse/OFFICE-1828
This commit only add this attribute to ODF import/export.
Engineering notation is not yet available.

Treat also thousand separator with exponent-interval
Change XML_NAMESPACE_NUMBER to XML_NAMESPACE_LO_EXT for
exponent-interval

Change-Id: Ia18f9e150ca32aa9bbe133c082c3f9330e949f11
Reviewed-on: https://gerrit.libreoffice.org/14875Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>