Some VTK optimizations in the Data Explorer

This PR needs some more work, **do not** merge!

After reading the [Catalyst User Guide](http://paraview.org/Wiki/images/4/48/CatalystUsersGuide.pdf) I found out that we are construction some VTK data structures not in the best way.

- [ ] Use `SetXXX()` instead of `InsertXXX()` for inserting points, cells, id, and field data (see pages 25, 30, and 34).
- [ ] Make sure to to proper delete ref-counted objects (see page 23 and 67)