added 2 way communication for latest block on external api

lib/collection.js

@@ -15,6 +15,19 @@ var Collection = function Collection(externalAPI)
 	return this;
 }
 
+Collection.prototype.setupSockets = function()
+{
+	this._externalAPI.on('connection', function (spark)
+	{
+		this._externalAPI.on('latestBlock', function (data)
+		{
+			spark.emit('latestBlock', {
+				number: this._highestBlock
+			});
+		});
+	});
+}
+
 Collection.prototype.add = function(data, callback)
 {
 	var node = this.getNodeOrNew({ id : data.id }, data);