Remove unused default element

Change-Id: I703f54ef8640f9be70f16441c330e53fce3f7489
DOC export: factor out wrap polygon handling to to sw::util

So that it'll be possible to reuse it in the DOCX exporter.

Change-Id: Ib7371c92c4fd93d7c6f3271ca81311bac8f1a1a7
DOCX export: handle wrap polygon around pictures

Change-Id: I83d9d42cd48ba4dcd86c6506c7dbd6493bb4d204