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.

cmd/web-handlers.go

@@ -741,6 +741,7 @@ type ListAllBucketPoliciesArgs struct {
 
 // BucketAccessPolicy - Collection of canned bucket policy at a given prefix.
 type BucketAccessPolicy struct {
+	Bucket string              `json:"bucket"`
 	Prefix string              `json:"prefix"`
 	Policy policy.BucketPolicy `json:"policy"`
 }
@@ -770,8 +771,11 @@ func (web *webAPIHandlers) ListAllBucketPolicies(r *http.Request, args *ListAllB
 	}
 	reply.UIVersion = browser.UIVersion
 	for prefix, policy := range policy.GetPolicies(policyInfo.Statements, args.BucketName, "") {
+		bucketName, objectPrefix := urlPath2BucketObjectName(prefix)
+		objectPrefix = strings.TrimSuffix(objectPrefix, "*")
 		reply.Policies = append(reply.Policies, BucketAccessPolicy{
-			Prefix: prefix,
+			Bucket: bucketName,
+			Prefix: objectPrefix,
 			Policy: policy,
 		})
 	}
@@ -822,6 +826,23 @@ func (web *webAPIHandlers) SetBucketPolicy(r *http.Request, args *SetBucketPolic
 		return nil
 	}
 
+	_, err = json.Marshal(policyInfo)
+	if err != nil {
+		return toJSONError(err)
+	}
+
+	// Parse check bucket policy.
+	if s3Error := checkBucketPolicyResources(args.BucketName, policyInfo); s3Error != ErrNone {
+		apiErr := getAPIError(s3Error)
+		var err error
+		if apiErr.Code == "XMinioPolicyNesting" {
+			err = PolicyNesting{}
+		} else {
+			err = fmt.Errorf(apiErr.Description)
+		}
+		return toJSONError(err, args.BucketName)
+	}
+
 	// Parse validate and save bucket policy.
 	if err := objectAPI.SetBucketPolicy(context.Background(), args.BucketName, policyInfo); err != nil {
 		return toJSONError(err, args.BucketName)