Adding RXDestroyOnAwake

A super simple MonoBehaviour that just destroys itself (and its
children) when it awakes. I use it in the editor as a place to try out
prefabs that I don't want to appear when the game runs. There's probably
a better way to do this, but it works fine.
Making isVisible affect scale instead of alpha

This is related to issue #194

This will give better performance than the current isVisible
implementation without having any foreseeable drawbacks.