Export object according to the given export profile and itemMimeType. The
default implementation allows to export objects in the format
application/xml or application/x-excel. The default implementation recursively walks
the object (composites and references objects) according to the reference
Override this method for custom-specific export and rendering of objects. E.g.
a custom-specific implementation could work as follows:
Derive the document type / template from the export profile.
Generate an XML according to the document type and object.
Invoke a (remote) rendering engine with the parameters:
document type (or exportProfile.template if the document templates are not stored in the rendering engine)