Pixels per meter update

Here are three unrelated commits I'm putting together in this pull request. The real important one is the pixelsPerMeter update.

The use-case I have is a top-down sport game where the arena's meter size is proportional to the number of players, and this requires pixelsPerMeter to behave properly when updated in the middle of a scene.
Ah, just one small thing here is that it would be good to make this connection before the signal emission, because someone may be crazy enough to change the pixelsPerMeter variable in response to the signal and then it would fail to update this body. But maybe I'm crazy to consider this scenario...