oox: allow to declare the wps namespace on export

Change-Id: I278b568d512dfbc34d24c612c1a532315e35e808
DOCX export: number drawingml objects from one

For some reason for drawingml shapes Word doesn't like the "0"
identifier. Let's do the same trick that works for font identifiers
already.

Change-Id: I30ebc33ab927becc1bbf146577eb36b914bf7edb