New: Replace react-tether with react-popper (#789)

frontend/src/Components/Portal.js

@@ -0,0 +1,18 @@
+import PropTypes from 'prop-types';
+import ReactDOM from 'react-dom';
+
+function Portal(props) {
+  const { children, target } = props;
+  return ReactDOM.createPortal(children, target);
+}
+
+Portal.propTypes = {
+  children: PropTypes.node.isRequired,
+  target: PropTypes.object.isRequired
+};
+
+Portal.defaultProps = {
+  target: document.getElementById('portal-root')
+};
+
+export default Portal;