Detect CocoonJS.App

There's a bit of a story behind this, but I'll try to keep it short.

While I've been working on a patch to detect Cordova's 'pause' and 'resume' events for Phaser.Stage's checkVisibilityChange(), I came across this [thread] (http://www.html5gamedevs.com/topic/8834-cocoonjs-pause-game-on-app-switch/) over on the forum. My hope, at the time, was that someone else would come along and write this patch and I could use their work to finish my own code. But, since that hasn't happened yet (and might never), I'm sending in this PR first for the check that establishes a 'game.device.cocoonJSApp' boolean that I plan to use later.