ENYO-2818: fix floating layer destruction issues

This change MAY NOT be ready for integration, but I wanted to start discussion.

We've had a recurring problem with popups where we generate a floating layer as a child of document.body when we've arleady rendered a enyo kind instance to document.body.  Then, the dev goes back to rerenders the kind or renders a different kind instance, and the floating layer is blown away.

This would fix that by having any code that renders into document.body instead render into a special div we create there.  This means we'd never stomp on all of the DOM nodes again, but I'm not entirely sure this works right with all the styling we do or acceleration.