Update JS target: Haxe 3.0 compatibility.
Improve Hammer.js externs
- Fix argument error in untyped js.
- Map to proper event class and typedefs
GestureEvents backed by Hammer.js
Small JS target fixes. Wrap unimplemented: Asset.
Only position using CSSMatrix, to fix transition
 issues on some Android browsers.

- Webkit only (for now)
Reduce reflows by hiding from DOM,
 instead of removing an element immediately.