App: add "Expanded" to DocumentObject.State

Looks like it was impossible to figure out if tree item of object is
expanded or collapsed. Now, it can be queried by e.g. `"Expanded" in
App.ActiveDocument.Fusion.State`

src/App/DocumentObjectPyImp.cpp

@@ -162,6 +162,9 @@ Py::List DocumentObjectPy::getState(void) const
         uptodate = false;
         list.append(Py::String("Restore"));
     }
+    if (object->testStatus(App::Expand)){
+        list.append(Py::String("Expanded"));
+    }
     if (uptodate) {
         list.append(Py::String("Up-to-date"));
     }