Use template literals instead of string concatenation (#3066)

We have used it inconsistently till now. Template literals are more
modern and easier to maintain in my opinion.

Because that's a large amount of changes, here's a way to reproduce it:
I added the rule `"prefer-template": "error"` to the `.eslintrc.json`
and did an autofix. Since this caused a new problem in line 409 of
`newsfeed.js`, I reversed it in that line and also removed the rule from
the eslint config file.

The rule is described here:
https://eslint.org/docs/latest/rules/prefer-template

Note: I've played around with some other linter rules as well, and some
seem to point to some specific, non-cosmetic, issues. But before I dive
even deeper and then introduce even bigger and hardly understandable
changes at once, I thought I'd start with this simple cosmetic rule.

serveronly/index.js

@@ -4,5 +4,5 @@ const Log = require("logger");
 app.start().then((config) => {
 	const bindAddress = config.address ? config.address : "localhost";
 	const httpType = config.useHttps ? "https" : "http";
-	Log.log("\nReady to go! Please point your browser to: " + httpType + "://" + bindAddress + ":" + config.port);
+	Log.log(`\nReady to go! Please point your browser to: ${httpType}://${bindAddress}:${config.port}`);
 });