Fixes #154 useAnimationLoop disabled in chrome.

Conflicts:
	leap.min.js
Only run animation loop if focused

This improves performance when multiple tabs are open, as chrome we
provide animationFrames for any window visible, even if out of focus,
LeapJS only needs to update if focus is given.  This improved by a
noticeable 5 FPS (15 to 20) with unfocused visible windows.

Note that when focus is returned, the focus event is fired before
resuming the animation loop.
Only run the pipeline on animation frames in the browser

This is pretty important, as the pipeline can be heavy and even include
calls for rendering to the GPU.  It does mean that if someone is needs
to do data analysis on deviceFrames directly, they won't have the same
processed frames available to them.  This isn't a problem until its a
problem.
Explicitly name leap animation frame callback for nicer profiling
Merge branch 'master' into requestAnimationFrame

Conflicts:
	leap.min.js
Merge pull request #155 from leapmotion/requestAnimationFrame

Fixes #154 useAnimationLoop disabled in chrome.