Switched from scaleZ to translateX to form stacking contexts: scaleZ butchered font rendering

@dinhviethoa

You were right, -webkit-transform:scaleZ(1) was for some reason butchering font smoothing, at least on Mac. -webkit-transform:translateX(0) achieves the same effect in terms of forming a stacking context, but leaves fonts alone.

I've turned -webkit-font-smoothing:auto back on for the editor too.

![screen shot 2014-05-28 at 2 04 48 am](https://cloud.githubusercontent.com/assets/5606182/3102482/8595a554-e647-11e3-8ffb-9e094470ec32.png)