Hygiene: Move class name generation to browser.js

* Apply all classes to the viewport tag rather than the body tag for consistency
* Include ipod in test for ios devices
* Remove ios class and replace it with overlay-ios
* Kill wgMFEnableCssAnimations

Change-Id: I9d1ff1725ba43956d1b7f1f9c2732ce9b2e80392
Merge "Hygiene: Move class name generation to browser.js"