New: Cleanup UI tooling, Update to Webpack 4, Gulp 4 (#655)

* New: Webpack 4

* New: Gulp 4

* New: Transpile UI for old browsers

Co-Authored-By: Mark McDowall <markus101@users.noreply.github.com>

frontend/src/Utilities/createAjaxRequest.js

@@ -1,6 +1,34 @@
 import $ from 'jquery';
 
-export default function createAjaxRequest(ajaxOptions) {
+const absUrlRegex = /^(https?:)?\/\//i;
+const apiRoot = window.Lidarr.apiRoot;
+
+function isRelative(ajaxOptions) {
+  return !absUrlRegex.test(ajaxOptions.url);
+}
+
+function moveBodyToQuery(ajaxOptions) {
+  if (ajaxOptions.data && ajaxOptions.type === 'DELETE') {
+    if (ajaxOptions.url.contains('?')) {
+      ajaxOptions.url += '&';
+    } else {
+      ajaxOptions.url += '?';
+    }
+    ajaxOptions.url += $.param(ajaxOptions.data);
+    delete ajaxOptions.data;
+  }
+}
+
+function addRootUrl(ajaxOptions) {
+  ajaxOptions.url = apiRoot + ajaxOptions.url;
+}
+
+function addApiKey(ajaxOptions) {
+  ajaxOptions.headers = ajaxOptions.headers || {};
+  ajaxOptions.headers['X-Api-Key'] = window.Lidarr.apiKey;
+}
+
+export default function createAjaxRequest(originalAjaxOptions) {
   const requestXHR = new window.XMLHttpRequest();
   let aborted = false;
   let complete = false;
@@ -12,6 +40,14 @@ export default function createAjaxRequest(ajaxOptions) {
     }
   }
 
+  const ajaxOptions = { ...originalAjaxOptions };
+
+  if (isRelative(ajaxOptions)) {
+    moveBodyToQuery(ajaxOptions);
+    addRootUrl(ajaxOptions);
+    addApiKey(ajaxOptions);
+  }
+
   const request = $.ajax({
     xhr: () => requestXHR,
     ...ajaxOptions