added prototype for xrviewer

+       
+import ARCS from '../build/arcs.js';
+import * as THREE from '../deps/three.js/index.js';
+//import FrustumCamera from '../deps/three.js/frustumcamera.js';
+        
+var XRViewer;
+
+/** 
+    * @class ARViewer 
+    * @classdesc Simple compositing viewer for augmented reality
+    */        
+XRViewer = ARCS.Component.create(
+    /** @lends ARViewer.prototype */
+    function () {
+        let renderer, scene3d, camera3d;
+        let sceneId;
+        
+        
+        // scenegraph initializations
+        scene3d = new THREE.Scene();
+
+        /**
+            * Initializes the widgets (HTML elements) needed as a basis 
+            * for the viewer.
+            * @param cName {string} id of the container that will enclose the scene renderer
+            * @param vName {string} id of the element at the source of the video stream
+            * @slot
+            * @function ARViewer#setWidgets
+            */
+        this.setWidgets = function() {
+
+            renderer = new THREE.WebGLRenderer();
+            renderer.setClearColor(0x000000, 1);
+            renderer.setSize(container.width, container.height);
+            container.appendChild(renderer.domElement);
+
+            var theta = 45;
+            camera3d = new THREE.PerspectiveCamera(theta, container.width / container.height, 0.01, 10);
+            scene3d.add(camera3d);
+
+            var _light = new THREE.DirectionalLight(0xffffff);
+            _light.position.set(0,5,5);
+
+            scene3d.add(_light);
+            updateAspectRatio();
+        };
+
+        /**
+            * Adds new objects to the current 3D scene
+            * @param scene {object} 3D object as defined by Three.js to add to the scene.
+            * @slot
+            * @function ARViewer#addScene
+            */
+        this.addScene = function (scene) {
+            scene3d.add(scene);
+        };
+    
+        /**
+            * Removes an object from the current 3D scene
+            * @param scene {object} 3D object as defined by Three.js to remove from the scene.
+            * @slot
+            * @function ARViewer#removeScene
+            */
+        this.removeScene = function (scene) {
+            scene3d.remove(scene);
+        };
+        
+        /**
+            * Triggers the rendering of the composite scene
+            * @function ARViewer#render
+            * @slot
+            */
+        this.render = function () {
+            renderer.autoClear = false;
+            renderer.clear();
+            renderer.render(scene3d, camera3d);
+        }
+        
+    },
+    /** @lends ARViewer.slots */
+    [
+        'setWidgets','setFocal','viewAll','setSize','addScene',
+        'resetCamera','removeScene','render','keepAspectRatio',
+        'setExtrinsics', 'setIntrinsics'
+        
+    ],
+    []
+);
+
+export default {XRViewer: XRViewer}; 
+