feat(external_api): make sure the created iframe has no border

modules/API/external/external_api.js

         this.frame.width = '100%';
         this.frame.height = '100%';
         this.frame.setAttribute('allowFullScreen', 'true');
+        this.frame.style.border = 0;
         this.frame = this.iframeHolder.appendChild(this.frame);
     }