App: GeoFeature/ComplexGeoData API changes

These are the bare minimum set of APIs for future new topogical naming
feature (see [here](https://git.io/fj6hy) for a overview of the new
APIs).

These APIs are added early to avoid too much code change for the new
features introduced in the current patch set.

src/App/ComplexGeoDataPy.xml

@@ -37,5 +37,11 @@
 		  </Documentation>
 		  <Parameter Name="Matrix" Type="Object" />
 	  </Attribute>
+      <Attribute Name="Tag">
+          <Documentation>
+              <UserDocu>Geometry Tag</UserDocu>
+          </Documentation>
+          <Parameter Name="Tag" Type="Int"/>
+      </Attribute>
   </PythonExport>
 </GenerateModel>