Optimize hit-testing and fix Simplebutton-related bugs. r=tobytailor

And fix bug with incorrect transform application in hitTestState.

This isn't ideal as it overrides an AS3-visible function in AS3-invisible ways and is hence quite dirty, but it works for now. I added a TODO for a better solution.

@tobytailor, can you quickly check if this seems ok and, if so, merge it?