Android stock browser check

This is a class-static function of Phaser.Device to check wether we’re
running on an Android Stock browser. Autors might want to scale down on
effects and switch to the CANVAS rendering method on those devices.
Usage: var defaultRenderingMode = Phaser.Device.isAndroidStockBrowser()
? Phaser.CANVAS : Phaser.AUTO;
Merge pull request #989 from lucbloom/android-stock-browser

Android stock browser check