sxw imp patch: page setup

Hello,

the attached patch adds the import of page setup (paper format, margins,
orientation) to the OpenWriter importer. A few FIXME remain where i have to
investigate more complex documents. The sxw file format is somewhat complex
handling stuff at times. However, all my more or less simple documents work.

In addition to that sxw section ends are detected and imported, the structure of
the document in Abi matches wrt. sections.

I'm amazed how useful Abi's codebase is for getting stuff done.

Regards,
Rob