Minor tweaks to the head tag

Inside of our head tag, we will want to change title, and because we renamed canvas.css to webgl.css, we will need to point our link tag to the new stylesheet name. Here are the only two tags that must change at the beginning of the HTML:

<title>WebGL Shell</title>
<link href="webgl.css" rel="stylesheet" type="text/css">

Later in the HTML, we will remove the img tag where the src is set to "spaceship.png". It is not strictly necessary to do this. In the canvas version, we were using this tag to render an image to the canvas. In this WebGL version, we will load the image dynamically, so it is not necessary to keep it around, but if you forget to remove it, having it there will not harm the app in any way.