Translate 3D Support for DOM

Adds translate3d support to the DOM backing view. This should give desktop builds slightly better performance.

Adds a :position(x, y) method to abstract "top/left" vs "translate3d(x,y)". Checks for support and detects correct prefix.

Falls back to top/left if it cannot be done. This means IE10, FF10+, Chrome 20+ and Safari 5+ all now support translate3d.
Update ViewBacking.js

Edited a typo/missed variable.
Merge pull request #4 from austinh/patch-1

Translate 3D Support for DOM