libmsooxml: updated processing of the graphicFrame element.

* The graphicFrame/graphic/graphicData element MAY contain a
group of graphic objects, which requires a draw:g element
instead of draw:frame as the containing frame.

* Updated docx/xlsx/pptx filter.

TODO:
docx/pptx: The tranformation and coordinates of child
custom-shape elements in the containing frame are wrong.
Seems we don't respect the group coordinates.

xlsx: A filter specific graphic style for the containing element
is required.