Implement OOXML vert attribute as WritingMode property

[Regina Henschel]

Hi all, hi Miklos,

To be able to save the info about OOXML vert attribute to ODF my idea is 
to use interally the WritingMode property and than write that as 
style/loext:writing-mode to graphic-properties in ODF. That would be the 
same as it is now done with the text directions of frames. It would 
allow odt->docx with keeping the text directions for shapes.

Currently the OOXML vert attribute is internally represented in the 
"TextPreRotateAngle" in "CustomShapeGeometry".

I first thought, that I could make WritingMode parallel to 
TextPreRotateAngle. But that breaks in several places. So my next try 
would be to use only WritingMode for the vert attribute. 
TextPreRotateAngle would be still used for "upr" and "grav" attribute 
value of diagram (SmartArt).

But that will be a larger change, so I ask before I continue work, 
whether you will agree to that attempt.

In case you say, "Do not touch that area", do you have another idea how 
to bring OOXML vert attribute to ODF?

Kind regards
Regina