demo: Disable animation by default

When using auto-LOD mode it can be distracting; we now disable the
animation playback by default, but make it easy to unpause/pause it with
a checkbox.

demo/simplify.html

@@ -63,6 +63,7 @@
 
 			var settings = {
 				wireframe: false,
+				animate: false,
 				pointSize: 1.0,
 				ratio: 1.0,
 				debugOverlay: false,
@@ -108,6 +109,7 @@
 			var gui = new GUI({ width: 300 });
 			var guiDisplay = gui.addFolder('Display');
 			guiDisplay.add(settings, 'wireframe').onChange(update);
+			guiDisplay.add(settings, 'animate').onChange(update);
 			guiDisplay.add(settings, 'pointSize', 1, 16).onChange(update);
 			guiDisplay.add(settings, 'debugOverlay').onChange(simplify); // requires debug data rebuild
 
@@ -541,7 +543,7 @@
 			}
 
 			function animate() {
-				if (mixer) {
+				if (mixer && settings.animate) {
 					mixer.update(clock.getDelta());
 				}