This PR turned into quite the upgrade for the code of the website. There should be no changes in design or content, but a number of improvements have been made:

• Gatsby V4. The website is now updated from Gatsby 3 to 4, which should make the build process a lot faster and the local development experience nicer.
• Node 16. The website didn't have a stated Node version, but was running with Node 12 in the GitHub Actions. The repo now has a .nvmrc file stating the Node version, and the GitHub Actions have been upgraded to use same version: Node 16.
• Updated packages. I have updated most packages to their newest versions. Since Gatsby doesn't support ESM packages yet, I had to keep some packages one version below their newest, but there are no dependency issues and everything seems to work.
• Better build process. I optimized the way we generate nodes in the build process, so we don't generate duplicate content. I also changed the way we save the name field in every node to not include the locale, which makes the logic easier on many of the pages when it comes to translations.
• New hooks. I implemented two news hooks to be used for translated content: useTranslations and useTranslationsWithEnglishBase. They are both documented and used on some pages. As we get ready to publish the first real translation, they might be used even more.
• Spanish translation files. This PR also adds a bunch of files for the Spanish translation. I currently disabled the translation, so the files won't get used and the build process will not slow down. As we get closer to finishing the translation, it will be very easy to enable it again.
• Fix libraries search. The libraries search had a problem where categories would shuffle around. I fixed it while making a more friendly version of the useFilteredArray hook.
• Fix build issue for examples. There was a build issue where the site would sometimes fail when building. This was because the examples would sometimes mistakenly try to load the png file instead of the json file in the example folder, and this would lead to an error when trying to read the JSON. This has been fixed and the site should build now.

@SableRaf This is a rather large pull request, and I have tested it as much as I can. If you could give it a good look on your local computer, that would make me feel a lot better. Here are the steps for making it run:

• Make sure you're running Node 16. I use nvm for this.
• Delete your node_modules folder
• Run npm install
• Then run npm run dev

Let me know if you run into any issues!

This fixes #317