On the fly sorting of object hierarchy in the UI

Hi,

Currently, the object hierarchy will not be updated in the UI unless you reload the editor. It shows when you try to change the parent of an object.

This fix just tweaks the sceneGraphChanged signal callback added by Sidebar.Scene.

Worth noting that due to the way UI.FancySelect.prototype.setOptions works, we have to swap around the IDs of ThreeJS objects that are meant to be listed. (ID, not UUID fortunately!)
There is no adverse effect to doing this in the editor app since it never relies on a given object having a given id.

The alternative is to tweak ui.js but I refrained since it looked as though you weren't the author (?)