Refactor bucket delete and bucket policy (#5580)

This commit adds the bucket delete and bucket policy functionalities
to the browser.

Part of rewriting the browser code to follow best practices and
guidelines of React (issues #5409 and #5410)

The backend code has been modified by @krishnasrinivas to prevent
issue #4498 from occuring. The relevant changes have been made to the
code according to the latest commit and the unit tests in the backend.
This commit also addresses issue #5449.

browser/app/js/buckets/Policy.js

@@ -0,0 +1,93 @@
+/*
+ * 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 { READ_ONLY, WRITE_ONLY, READ_WRITE } from '../constants'
+
+import React from "react"
+import { connect } from "react-redux"
+import classnames from "classnames"
+import * as actionsBuckets from "./actions"
+import * as actionsAlert from "../alert/actions"
+import web from "../web"
+
+export class Policy extends React.Component {
+  removePolicy(e) {
+    e.preventDefault()
+    const {currentBucket, prefix, fetchPolicies, showAlert} = this.props
+    web.
+      SetBucketPolicy({
+        bucketName: currentBucket,
+        prefix: prefix,
+        policy: 'none'
+      })
+      .then(() => {
+        fetchPolicies(currentBucket)
+      })
+      .catch(e => showAlert('danger', e.message))
+  }
+
+  render() {
+    const {policy, prefix} = this.props
+    let newPrefix = prefix
+
+    if (newPrefix === '')
+      newPrefix = '*'
+
+    return (
+      <div className="pmb-list">
+        <div className="pmbl-item">
+          { newPrefix }
+        </div>
+        <div className="pmbl-item">
+          <select className="form-control"
+            disabled
+            value={ policy }>
+            <option value={ READ_ONLY }>
+              Read Only
+            </option>
+            <option value={ WRITE_ONLY }>
+              Write Only
+            </option>
+            <option value={ READ_WRITE }>
+              Read and Write
+            </option>
+          </select>
+        </div>
+        <div className="pmbl-item">
+          <button className="btn btn-block btn-danger" onClick={ this.removePolicy.bind(this) }>
+            Remove
+          </button>
+        </div>
+      </div>
+    )
+  }
+}
+
+const mapStateToProps = state => {
+  return {
+    currentBucket: state.buckets.currentBucket
+  }
+}
+
+const mapDispatchToProps = dispatch => {
+  return {
+    fetchPolicies: bucket => dispatch(actionsBuckets.fetchPolicies(bucket)),
+    showAlert: (type, message) =>
+      dispatch(actionsAlert.set({ type: type, message: message }))
+  }
+}
+
+export default connect(mapStateToProps, mapDispatchToProps)(Policy)