Add green flag skeleton component

src/components/green-flag.js

+const React = require('react');
+
+class GreenFlag extends React.Component {
+    constructor (props) {
+        super(props);
+        this.onClick = this.onClick.bind(this);
+    }
+    onClick (e) {
+        e.preventDefault();
+        this.props.vm.greenFlag();
+    }
+    render () {
+        return (
+            <div className="scratch-green-flag">
+                <button onClick={this.onClick}></button>
+            </div>
+        );
+    }
+}
+
+GreenFlag.propTypes = {
+    vm: React.PropTypes.object
+};
+
+module.exports = GreenFlag;

src/components/gui.js

 const React = require('react');
 
 const Blocks = require('./blocks');
+const GreenFlag = require('./green-flag');
 const Renderer = require('scratch-render');
 const SpriteSelector = require('./sprite-selector');
 const Stage = require('./stage');
@@ -38,6 +39,7 @@ class GUI extends React.Component {
     render () {
         return (
             <div className="scratch-gui">
+                <GreenFlag vm={this.props.vm} />
                 <Stage stageRef={stage => this.stage = stage} />
                 <SpriteSelector vm={this.props.vm} />
                 <Toolbox toolboxRef={toolbox => this.toolbox = toolbox} />