function GLTFLoader( manager ) {

        this.manager = ( manager !== undefined ) ? manager : THREE.DefaultLoadingManager;

    }
@author Rich Tibbett / https://github.com/richtr
@author mrdoob / http://mrdoob.com/
@author Tony Parisi / http://www.tonyparisi.com/
@author Takahiro / https://github.com/takahirox
@author Don McCurdy / https://www.donmccurdy.com