ol.overlay.Overlay can be used to bind DOM elements to a
coordinate on the map. It has positioning options to support
e.g. popups or image markers that have an anchor at the bottom
and an unknown size.
The overlayContainer stops propagation on mousedown and
touchstart events, so clicks and gestures on overlays don't
trigger any MapBrowserEvent. To make this work reliably, we now
only fire dblclick in mapbrowserevent.js when there was a
previous mousedown or touchstart. The default container for
controls is now the overlayContainer.
Adding a new DragBox control and using it in the shiftdragzoom interaction to provide visual feedback of the zoom box. The control is nicely separated from the interaction - it only draws the box and does not perform any action.
