Add the beginnings of the hierarchy panel in the scene editor.
Add a function to the scripting environment for retrieving pointers to the scene nodes contained in the scene editor.
Add a change that was meant to be included in the previous commit.
Add the ability to retrieve the ID of a scene node via the scripting environment.
Removed some redundant code.
Add the basics to the hierarchy panel in the scene editor and fix a few bugs in the process.

This is still largely incomplete. All it does is show a flat list of the current scene nodes and nothing else.