use debounce function on map moveend zoomend

[stefanocudini]

        function debouncer(func, timeout) {
            var timeoutID;
            timeout = timeout || 300;
            return function () {
                var scope = this , args = arguments;
                clearTimeout( timeoutID );
                timeoutID = setTimeout( function () {
                    func.apply( scope , Array.prototype.slice.call( args ) );
                }, timeout);
            };
        }