Added history tracebacks to the SceneInspector.

These are available from the right click context menu for any value displayed in the the SceneInspector. I've marked this as fixing #834, but it doesn't support showing changes in location introduced by nodes like Group, Instancer or Duplicate. I'm not sure whether or not Caribou exposes such nodes, or how big a deal this is. I'd definitely like to add the necessary API changes to support this because I'll want them for the transform manipulators I'm doing in my spare time, but I don't know whether or not it's an IE priority. Either way, I suggest we make another ticket for that part...