n#821567: Import PPTX background images with table-name.

Ported from 2ec4d410de5bd98527336a9dc49abb76656373df

Change-Id: I50693f7fea8de4f1d3668378aa2334539dd80c42
Reviewed-on: https://gerrit.libreoffice.org/8546
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>