Implemented loading of shape groups. This was a little more work as the child shapes of the group had to be added to the document after loading so I put them into the loading context.

After loading the document, the apps KoShapeControllerBase implementaion has to transfer the collected shapes from the context to itself. The creation of the group shape is hardwired into the shape registry as we do not want a shape group appear inside the shape selector (when using a KoShapeGroupFactory).

Additionally I changed the shapes to save their global transformation matrix, as that is what they are in ODF.