helper method for script insertion

append_script_method.ts

private appendScript(host: HTMLElement, data: string, index: number) {
    this.ngZone.runOutsideAngular(() => {
      const script = document.createElement('script');
      script.type = 'text/javascript';
      script.charset = 'utf-8';
      script.id = this.vrScriptPrefix + index;
      script.defer = true;
      script.async = true;
      script.text = data;
      host.appendChild(script);
      // memorize the script so we can remove it later
      this.activeScripts.push(script);
    });
  }