Feature/grs 1955 change commonjs imports (#1995)

* GRS-1955: Using ES6 import/export in src files

* GRS-1955: Using ES6 import/export in test files

* GRS-1955: Using ES6 import/export in themes index.js

* GRS-1955: Readding blank line at end of top-languages-card.js

* feat: fix test es6 import errors

This commit makes sure jest is set-up to support es6. It also fixes
several test errors and sorts the imports.

* test: update test node version

This commit makes sure node 16 is used in the github actions.

* refactor: run prettier

Co-authored-by: rickstaa <rick.staa@outlook.com>

tests/renderStatsCard.test.js

@@ -1,13 +1,14 @@
-require("@testing-library/jest-dom");
-const cssToObject = require("@uppercod/css-to-object").cssToObject;
-const renderStatsCard = require("../src/cards/stats-card");
-
-const {
+import {
   getByTestId,
-  queryByTestId,
   queryAllByTestId,
-} = require("@testing-library/dom");
-const themes = require("../themes");
+  queryByTestId,
+} from "@testing-library/dom";
+import { cssToObject } from "@uppercod/css-to-object";
+import renderStatsCard from "../src/cards/stats-card";
+// adds special assertions like toHaveTextContent
+import "@testing-library/jest-dom";
+
+import { themes } from "../themes";
 
 describe("Test renderStatsCard", () => {
   const stats = {