DOCX drawingML export of textboxes: write <wps:bodyPr> in oox

It's possible to write this tag in oox (so it represents the properties
of the shape) or in sw (so it represents the properties of the shape's
textbox). Do the previous, as the textbox is really just a container in
this use case, nothing more.

If we are at it, also fix the default value of <wps:bodyPr>'s l/r/t/bIns
attributes.

Change-Id: I0571b9d8ea7dc0acd5c61f3e28e18400d305eab3