Refactor browser dropdown links and components (#5562)

* refactor browser links and about modal

Moved about modal to separate component and added unit tests.

* refactor change password modal component

* added unit tests for ChangePasswordModal

* fix logout function in browser dropdown

* remove older unused BrowserDropdown component

* remove unused variables from BrowserDropdown component

* show BrowserDropdown and StorageInfo only for LoggedIn users

Non-loggedIn users will see a 'Login' button

browser/app/js/browser/__tests__/AboutModal.test.js

@@ -0,0 +1,41 @@
+/*
+ * Minio Cloud Storage (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import React from "react"
+import { shallow } from "enzyme"
+import { AboutModal } from "../AboutModal"
+
+describe("AboutModal", () => {
+  const serverInfo = {
+    version: "test",
+    memory: "test",
+    platform: "test",
+    runtime: "test"
+  }
+
+  it("should render without crashing", () => {
+    shallow(<AboutModal serverInfo={serverInfo} />)
+  })
+
+  it("should call hideAbout when close button is clicked", () => {
+    const hideAbout = jest.fn()
+    const wrapper = shallow(
+      <AboutModal serverInfo={serverInfo} hideAbout={hideAbout} />
+    )
+    wrapper.find("button").simulate("click")
+    expect(hideAbout).toHaveBeenCalled()
+  })
+})