Add a webgl button to the demo

demo/client.ts

@@ -45,8 +45,6 @@ let socketURL;
 let socket;
 let pid;
 
-(<any>window).webgl = () => term.loadAddon(new WebglAddon());
-
 const terminalContainer = document.getElementById('terminal-container');
 const actionElements = {
   findNext: <HTMLInputElement>document.querySelector('#find-next'),
@@ -91,6 +89,7 @@ if (document.location.pathname === '/test') {
 } else {
   createTerminal();
   document.getElementById('dispose').addEventListener('click', disposeRecreateButtonHandler);
+  document.getElementById('webgl').addEventListener('click', () => term.loadAddon(new WebglAddon()));
 }
 
 function createTerminal(): void {

demo/index.html

@@ -36,6 +36,7 @@
     <hr/>
     <p><strong>Attention:</strong> The demo is a barebones implementation and is designed for the development and evaluation of xterm.js only. Exposing the demo to the public as is would introduce security risks for the host.</p>
     <button id="dispose" title="This is used to testing memory leaks">Dispose terminal</button>
+    <button id="webgl"">Enable WebGL Renderr</button>
     <script src="dist/client-bundle.js" defer ></script>
   </body>
 </html>