...at least when we can easily not assume it.

shapes = shapes of the same XShapes
an enumeration = it is the sequence 0, 1, 2, 3, ..., XShapes->getCount()-1

We replace the ZOrder property by the index of the XShape in the
XShapes (the same XShapes that is passed to seekShapes()... when that
is easy to find. Else, use ZOrder and hope for the best.

ZOrders are not always an enumeration. For example, in documents
(forms) created by the Base forms wizard, it is not the case.

The wrong assumptions was leading to the following bugs in the Base
form wizard:

 - Only the first two controls in the form were successfully saved. The
   others were just dropped.

 - Whereas the labels had the proper style (background and text
   colour) applied while creating the document, these were not saved
   successfully

Change-Id: I15b9a3ef3b16eafa9698332e35d82d51d51627f8