Rename ol.Observable#dispatchChangeEvent() to #changed()

Since dispatchChangeEvent does not only dispatch a change event, but
also increases the revision counter, the method name should reflect
this.

examples/geolocation-orientation.js

@@ -220,7 +220,7 @@ function simulatePositionChange(position) {
       'EPSG:3857');
   geolocation.set('position', projectedPosition);
   geolocation.set('speed', coords.speed);
-  geolocation.dispatchChangeEvent();
+  geolocation.changed();
 }
 
 function disableButtons() {