Save and restore auto-possessed controller sensor, and spawn location for scenes

Kind of a niche one... Right now, persistent variables, the last scene, and the doorway used to enter it are saved and restored when you come back to the dream.

Normally when you enter a scene it auto-possesses an object with a controller sensor of the same name as was possessed when leaving the previous scene. That object is then moved to the doorway they came in by. This is not saved and restored between sessions, however.

So if the creator leaves their character in some random place, that's fine if the player plays through all in one go. But if they leave the dream at that point and come back, their character will be in some random place instead of spawning at the doorway that activated.

This isn't a "bug" really, but I feel like this behaviour would be expected by creators and players. And could cause trouble for people who have multiple entrances into their scene.