reduce calls to _render() caused by jumpTo()

[NathanMOlson]

1. Set fadeDuration to 0.
2. Don't call _render() on 'move' event
3. On 'moveend' event, only call _render() if all tiles are loaded
4. On 'data' event, only call _render() if all tiles are loaded
5. If _placementDirty is true, a re-render will be required. In this case, return from _render() early, before the expensive call to painter.render()