impr: changed "undefined" as default value for unused attributes in models (close #8)

Author: JohnnyTheTank

demo/aping-config.js

@@ -3,7 +3,7 @@ apingApp.config(['$provide', function ($provide) {
 
     $provide.constant("apingApiKeys", {
         twitter: [
-            {'bearer_token':"AAAAAAAAAAAAAAAAAAAAACs3iwAAAAAA%2BH8LdT7YfKIzk8fvQvqKvoePuxo%3DMKfXX2ojtacGL8aOLAhlBDUrEFpy0DUuiyebet22Wa2YVrX7cc"}
+            {'bearer_token':"<YOUR_BEARER_TOKEN>"},
         ],
     });