Local Overlay Stacks

After a spirited discussion, localOverlay is getting some children.

* localOverlayBlockers - UI elements that are meant to prevent
interaction with the element. This includes Phantoms and
Highlights.

*localOverlayControls - UI elements that are meant to be
interacted with in order to modify the element. This includes
resize handles and drag marker.

*localOverlayMenus - UI elements that should always position
above all other controls. This includes the context menu.

Bug: 50159
Change-Id: Ic69c2ad275389a31c9fbaf47f3665dcdbb7ac2af