Add enyo.dom.addBodyClass method that defers settings any classes until app is rendered
Modify code that uses document.body to use this.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #424 from enyojs/enyo-dom-addBodyClass

GF-12279: Add enyo.dom.addBodyClass method that defers settings any classes until ...