DOCX drawingML import: handle paragraph top margin

Change-Id: I4a69647af5b068c35bea0a5f9665a5e68eb76293
DOCX drawingML export: fix paragraph margins

Without the EndParagraphProperties() call, w:spacing wasn't ever
written as a paragraph property.

Change-Id: Iff4ca2a9e0725ac38d7b528c220c8ea58fc89cab