fix(ui): polyfill fetch()

This allows it to run on all browsers from the browserslist config

ui/package.json

@@ -43,7 +43,8 @@
     "react-resize-detector": "3.1.3",
     "react-scripts": "2.0.4",
     "react-select": "2.1.0",
-    "react-transition-group": "2.5.0"
+    "react-transition-group": "2.5.0",
+    "whatwg-fetch": "3.0.0"
   },
   "scripts": {
     "start": "NODE_ENV=dev REACT_APP_BACKEND_URI=http://localhost:8080 react-scripts start",

ui/src/index.js

@@ -2,6 +2,9 @@
 // https://babeljs.io/docs/en/babel-polyfill#usage-in-node-browserify-webpack
 import "@babel/polyfill";
 
+// fetch() polyfill for IE and some mobile browsers
+import "whatwg-fetch";
+
 import React from "react";
 import ReactDOM from "react-dom";