fix (PersistenceItem) no type casting for persistence items

Author: vengrov

lib/server-code/api/persistence-item.js

@@ -3,6 +3,10 @@
 const Backendless = require('backendless');
 
 function promisify(fn, context) {
+  if (Backendless.promisesEnabled()) {
+    return fn.bind(context);
+  }
+  
   return function() {
     return new Promise((resolve, reject) => {
       const args = Array.prototype.slice.call(arguments);
@@ -64,14 +68,14 @@ class PersistenceItem {
    * @private
    */
   get dataStore() {
-    return Backendless.Data.of(this.___class);
+    return Backendless.Persistence.of(this.constructor);
   }
 
   /**
    * @private
    */
   static get dataStore() {
-    return Backendless.Data.of(this.name);
+    return Backendless.Persistence.of(this);
   }
 
   /**