Add green flag and stop button to playground

playground/index.html

@@ -9,8 +9,11 @@
 </head>
 <body>
     <div id="vm-devtools">
+        <h2>Scratch VM Playground</h2>
+        <button id="greenflag">Green flag</button>
+        <button id="stopall">Stop</button>
         <div id="tab-blockexplorer">
-            <h2>VM Block Representation</h2>
+            <h3>VM Block Representation</h3>
             <pre id="blockexplorer"></pre>
         </div>
     </div>

playground/playground.css

@@ -20,7 +20,7 @@ body {
 #blockexplorer {
     position: absolute;
     width: 100%;
-    height: 80%;
+    height: 75%;
     overflow: scroll;
     border: 1px solid #fff;
     background: rgb(36,36,36);

playground/playground.js

@@ -23,4 +23,12 @@ window.onload = function() {
 
     // Run threads
     vm.runtime.start();
+
+    // Handlers for green flag and stop all.
+    document.getElementById('greenflag').addEventListener('click', function() {
+        vm.runtime.greenFlag();
+    });
+    document.getElementById('stopall').addEventListener('click', function() {
+        vm.runtime.stopAll();
+    });
 };