Vendorize with bug fixes from minio browser. (#3341)

This patch brings in changes from miniobrowser repo.

- Bucket policy UI and functionality fixes by @krishnasrinivas
- Bucket policy implementation by @balamurugana
- UI changes and new functionality changing password etc. @rushenn
- UI and new functionality for sharing URLs, deleting files
  @rushenn and @krishnasrinivas.
- Other misc fixes by @vadmeste @brendanashworth

cmd/object-errors.go

@@ -325,6 +325,13 @@ func (e NotImplemented) Error() string {
 	return "Not Implemented"
 }
 
+// PolicyNesting - policy nesting conflict.
+type PolicyNesting struct{}
+
+func (e PolicyNesting) Error() string {
+	return "New bucket policy conflicts with an existing policy. Please try again with new prefix."
+}
+
 // Check if error type is IncompleteBody.
 func isErrIncompleteBody(err error) bool {
 	err = errorCause(err)