Create Editor Gadget Examples

To facilitate the Qt Design Studio integration, we need to demonstrate how exactly we would implement gadgets.  In this context gadgets are helper widgets in 3D to facilitate the editing of 3D scenes.  For example the translate, rotation, and scale gadgets are used to modify the transform of the selected node.  These are rendered as 3D tools in the 3D scene that when touched and draged modify the transform.  These are visual aids which can either be rendered in local or global space.

It is also necessary to demonstrate which item or items are currently selected.  This can either be done by highlighting and item with an outline, or by rendering a bounding box around those items.

It also may be interesting to show a wire-frame mode for displaying certain items.

Since this is a feature that would be eventually integrated into Qt Design Studio, it is ok simply to implement these in a standalone example that can be referenced by the Qt Design Studio team for their implementation. This also validates we have all the necessary features they need.