Add CollapseButton component.

app/renderer/js/components/collapse-button.js

@@ -0,0 +1,37 @@
+'use strict';
+
+const BaseComponent = require(__dirname + '/../components/base.js');
+
+class CollapseButton extends BaseComponent {
+	constructor(props) {
+		super();
+		this.init();
+	}
+
+	init() {
+        this.sidebarShown = true;
+
+        this.$sidebar = document.getElementById('sidebar');
+        this.$el = document.getElementById('collapse-button');
+        this.$icon = this.$el.querySelector('i');
+
+		this.registerListeners();
+	}
+
+	registerListeners() {
+		this.$el.addEventListener('click', this.toggleSidebar.bind(this));
+	}
+
+    toggleSidebar() {
+        if (this.sidebarShown) {
+            this.$sidebar.classList.add('hidden');
+            this.$icon.innerHTML = 'keyboard_arrow_right';
+        } else {
+            this.$sidebar.classList.remove('hidden');
+            this.$icon.innerHTML = 'keyboard_arrow_left';
+        }
+        this.sidebarShown = !this.sidebarShown;
+    }
+}
+
+module.exports = CollapseButton;