Add support for Joist animationFrameListener

[samreid]

A number of situations are using requestAnimationFrame or setTimeout/setInterval instead of going through the main Sim.js requestAnimationFrame, which could cause problems for scenery input event recording. We should create a Joist module that can be loaded and used like addStepListener(function(dt){})

[samreid]

on Skype, @pixelzoom said:

[10/8/2013 2:00:31 PM] Chris Malley: seems to be working as expected. thanks!

Closing.