Optimized Resources constructor

- this code has shown to be chronically slow, due to the `Object.assign`
- we don't really need this, as we can just use a normal assign in this
  case
- this cuts 15% CPU from boot time for sites with a lot of resources
  (posts)

ghost/core/core/server/services/url/Resource.js

@@ -13,13 +13,12 @@ class Resource extends EventEmitter {
     constructor(type, obj) {
         super();
 
-        this.data = {};
         this.config = {
             type: type,
             reserved: false
         };
 
-        Object.assign(this.data, obj);
+        this.data = obj;
     }
 
     /**