MS PowerPoint template format now supported not only for import,
but for export too.

Change-Id: Ib61798b5fe966b895ed850f4b4ad7d7d06740adc
Reviewed-on: https://gerrit.libreoffice.org/65475
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>