allow non-loggedin users to access public bucket (#5570)

* conditionally render main action buttons

- Make bucket action will be available only for loggedIn users
- File upload button will be avaialble for loggedIn users
  and non-loggedIn users if the prefix is writable

* select the bucket and prefix from the url

When the url contains bucket and prefix, it will be selected
by default instead of the first bucket from the list.

* show BucketSearch only for LoggedIn users

* allow non-LoggedIn users to access public bucket

* removed unused Router imports

* fix test case failures in BucketList.test.js

* remove dupicate minioBrowserPrefix from url

since history is already initialized with minioBrowserPrefix,
no need to use it in push or replace

* remove unused match from App component

* remove unused minioBrowserPrefix imports

browser/app/js/browser/Login.js

@@ -21,7 +21,6 @@ import logo from "../../img/logo.svg"
 import Alert from "../alert/Alert"
 import * as actionsAlert from "../alert/actions"
 import InputGroup from "./InputGroup"
-import { minioBrowserPrefix } from "../constants"
 import web from "../web"
 import { Redirect } from "react-router-dom"
 
@@ -46,7 +45,7 @@ export class Login extends React.Component {
         password: document.getElementById("secretKey").value
       })
       .then(res => {
-        history.push(minioBrowserPrefix)
+        history.push("/")
       })
       .catch(e => {
         showAlert("danger", e.message)
@@ -67,7 +66,7 @@ export class Login extends React.Component {
   render() {
     const { clearAlert, alert } = this.props
     if (web.LoggedIn()) {
-      return <Redirect to={minioBrowserPrefix} />
+      return <Redirect to={"/"} />
     }
     let alertBox = <Alert {...alert} onDismiss={clearAlert} />
     // Make sure you don't show a fading out alert box on the initial web-page load.