libmso: Improved support for rotated shapes (group shapes still not supported).

* For any but a child shape, the OfficeArtClientAnchor might contain a 90 degrees rotated
rectangle. It depends on the rotation angle, and the intervals differ between shape types.
It seems like a relict from times when only rotation in {0,90,180,270} was supported.

* Added support for flipping, using draw:mirror-vertical and draw:mirror-horizontal attributes
of the draw:enhanced-geometry element.

NOTE: At the moment rotation of simple shapes and their positioning into a group shape seems fine.
However rotation and flipping of the group shape is not supported. If someone has good knowledge
of this topic, then feel free to implement.