Animated zoom

Provide the ability to zoom with or without an animation effect thanks to @mgrewal1 work on her fork of Peaks.

What needs to be done:

- [x] to fix the zoom level issue
- [x] to spread a segment update (zoomview to overview)
- [x] `webkitRequestAnimationFrame` for Safari 6

![waveform-zoom-animation](https://cloud.githubusercontent.com/assets/138627/3473828/a48349d8-02dc-11e4-962c-13da400f33a8.gif)