Fix a bug in SceneNode where adding a component wouldn't always post the appropriate event.
Fix a selection bug in the scene editor where the picking volume was not being updated when a model component was attached.

This commit also brings the scene editor's physics simulation toggle up-to-date with the new state stack system.
Remove code that was supposed to have been removed in the previous commit.
Disable the physics simulation in the scene editor when an undo/redo operation is performed.
Fix a bug in DynamicsComponent deserialization where the scale of the collision was not being set properly.
Disable physics simulation before saving a scene in the scene editor.
Fix a TODO to update the icon of the Physics button in the scene editor.

The issue was that when the simulation was enabled or disabled by any means other than clicking the button, the icon was not being updated to reflect the change in state.
First of several commits working towards improving the memory management of scene nodes.

There is a crash in this commit which will be fixed by the end of this change.
Improve the way scene nodes are added and removed from a scene.

These new changes are a little more restrictive, but the code is much nicer and more intuitive.
Fix a memory leak in the scene state stack.

Specifically, this was due to the staging area not clearing itself in it's destructor.