Points: show now returns an GeoFeature object

* Added one return statement into try-catch block which returns the appropriate object (instead of `None`).
* Behaviour now in line with `Part.show`.

Example:

```Python
>>> import Points
>>> pp = Points.Points()
>>> pp.addPoints([(1,2,3),(4,5,6)])
>>> go = Points.show(pp)
>>> go  # Former behaviour was to return None
<GeoFeature object>
>>> go.ViewObject.ShapeColor = (1,0,0)
>>> go.ViewObject.ShapeColor = (1.,0.,0.)
>>> go.ViewObject.PointSize = 20
```

src/Mod/Points/App/AppPointsPy.cpp

@@ -398,6 +398,7 @@ private:
             Points::Feature* pcFeature = static_cast<Points::Feature*>(pcDoc->addObject("Points::Feature", name));
             // copy the data
             pcFeature->Points.setValue(*(pPoints->getPointKernelPtr()));
+	    return Py::asObject(pcFeature->getPyObject());
         }
         catch (const Base::Exception& e) {
             throw Py::RuntimeError(e.what());