Add z-axis label

[GoogleCodeExporter]

It would be nice to have the possibility to set a label for the z axis.
Something similar to the existing methods setXLabel() and setYLabel() e.g.

surfacePanel.getSurface().setXLabel("Mylabel");

Original issue reported on code.google.com by Filippak...@gmail.com on 27 Mar 2012 at 9:53