Storing topmost enyo controls into enyo.roots array on renderInto call

Reason: Along with being a generally useful thing to have, I need a reference to enyo tree root to de-componentalize Spotlight, namely to hook into top of the tree events and have a point of reference for tree traversal. 

Simply going from a given control up the chain can fail because some singletons, like FloatingLayer are indistinguishable from any other root (being a control and not having a parent)