Add app.utility to register utility functions by name

lib/application.js

@@ -243,6 +243,21 @@ app.connector = function(name, connector) {
   this.connectors[camelize(name)] = connector;
 };
 
+/**
+ * Register a utility function with the given name
+ *
+ * The utilities will be used to resolve functions by name so that functions can
+ * be referenced in JSON configuration files, for example, the default value
+ * function, the middleware handler, or the validator
+ * @param {String} name The utility name
+ * @param {Function} fn The handler
+ */
+app.utility = function(name, fn) {
+  assert(typeof name === 'string', 'Utility function name must be a string');
+  assert(typeof fn === 'function', 'The utility must be a function');
+  this.utilities[name] = fn;
+};
+
 /**
  * Get all remote objects.
  * @returns {Object} [Remote objects](http://apidocs.strongloop.com/strong-remoting/#remoteobjectsoptions).

lib/loopback.js

@@ -75,6 +75,8 @@ function createApplication() {
   app.connector('memory', loopback.Memory);
   app.connector('remote', loopback.Remote);
 
+  app.utilities = {};
+
   return app;
 }