Cleanup compliments module (#2965)

Lots of small fixes and cleanups:
- only render something when there is a compliment
- cleanup naming
- use es6 notations
- use fetch instead of XMLHttpRequest in compliments

Co-authored-by: veeck <michael@veeck.de>
Co-authored-by: Karsten Hassel <hassel@gmx.de>

tests/e2e/helpers/global-setup.js

@@ -35,6 +35,7 @@ exports.getDocument = () => {
 		const url = "http://" + (config.address || "localhost") + ":" + (config.port || "8080");
 		jsdom.JSDOM.fromURL(url, { resources: "usable", runScripts: "dangerously" }).then((dom) => {
 			dom.window.name = "jsdom";
+			dom.window.fetch = corefetch;
 			dom.window.onload = () => {
 				global.document = dom.window.document;
 				resolve();