## Add 3D camera orientation gizmo

The widget representation has shafts and
little spheres with text on them. The spheres always
follow the camera.

The widget representaion's orientation is synchronized with
the camera of the parent renderer.

To look down on any particular axis, simply click on
a handle.

To rotate the camera and get a feel of the camera orientation,
either move mouse in the renderer or click on a handle
and move it around.
