Add default loading managers

src/three/CMPTLoader.js

@@ -1,11 +1,11 @@
-import { Group } from 'three';
+import { Group, DefaultLoadingManager } from 'three';
 import { CMPTLoaderBase } from '../base/CMPTLoaderBase.js';
 import { B3DMLoader } from './B3DMLoader.js';
 import { PNTSLoader } from './PNTSLoader.js';
 
 export class CMPTLoader extends CMPTLoaderBase {
 
-	constructor( manager ) {
+	constructor( manager = DefaultLoadingManager ) {
 
 		super();
 		this.manager = manager;

src/three/I3DMLoader.js

@@ -8,7 +8,7 @@ const tempSca = new Vector3();
 const tempMat = new Matrix4();
 export class I3DMLoader extends I3DMLoaderBase {
 
-	constructor( manager ) {
+	constructor( manager = DefaultLoadingManager ) {
 
 		super();
 		this.manager = manager;

src/three/PNTSLoader.js

@@ -1,9 +1,9 @@
 import { PNTSLoaderBase } from '../base/PNTSLoaderBase.js';
-import { Points, PointsMaterial, BufferGeometry, BufferAttribute } from 'three';
+import { Points, PointsMaterial, BufferGeometry, BufferAttribute, DefaultLoadingManager } from 'three';
 
 export class PNTSLoader extends PNTSLoaderBase {
 
-	constructor( manager ) {
+	constructor( manager = DefaultLoadingManager ) {
 
 		super();
 		this.manager = manager;