Add example of showing a coordinate axis gizmo that tracks the main orientation

[dov]

This example show a coordinate axis in the upper right corner that tracks the rotation part of the model camera.

[dov]

@robertosfield I'm looking forward to your critique and code review. :-) Thanks for putting me on the right track.

[robertosfield]

The example looks good and is now merged with vsgExamples master. I changed the example to name vsgaxes and made a few minor tweaks to variables names and indentation. Thanks for the example :-)