Add click event as responsive alternative to singleclick

The singleclick event makes the application feel slow because
of the 250 ms delay that is used to rule out a dblclick.

examples/popup.js

@@ -60,7 +60,7 @@ var map = new ol.Map({
 /**
  * Add a click handler to the map to render the popup.
  */
-map.on('singleclick', function(evt) {
+map.on('click', function(evt) {
   var coordinate = evt.coordinate;
   var hdms = ol.coordinate.toStringHDMS(ol.proj.transform(
       coordinate, 'EPSG:3857', 'EPSG:4326'));