Add React Admin and modify AdminHandler

jsx/src/util/jhapiUtil.js

@@ -0,0 +1,10 @@
+export const jhapiRequest = (endpoint, method, data) => {
+  return fetch("/hub/api" + endpoint, {
+    method: method,
+    json: true,
+    headers: {
+      "Content-Type": "application/json",
+    },
+    body: data ? JSON.stringify(data) : null,
+  });
+};