add How-to & Signout modal

src/browser/main/controllers/modals/SignOutModalController.js

@@ -0,0 +1,13 @@
+/* global angular */
+angular.module('codexen')
+  .controller('SignOutModalController', function ($modalInstance) {
+    var vm = this
+
+    vm.submit = function () {
+      $modalInstance.close()
+    }
+
+    vm.cancel = function () {
+      $modalInstance.dismiss('cancel')
+    }
+  })