Translation management scripts

[a2br]

Here are the translation management files requested in issue https://github.com/NMF-earth/nmf-app/issues/225 and started in PR https://github.com/NMF-earth/nmf-app/pull/231, now fully operational. They have all been tested and are ready to use.

Changelog

Here is a recap of what has been changed in the following commits:

• group-translation-files.js has been created in scripts/poeditor. When executed, new JSON files will be created in the same dir for each language with all the corresponding translations in it (prettified with the native JSON.stringify function).
• spread-translation-files.js has been created in scripts/poeditor. When executed, the data in the JSON files created by the previous script will be copied into all the translation files across the repo.
• The scripts above have been executed (reference files created by group~, other files edited by spread~ (indentation changed).
• a quick guide has been written in README.md

[a2br]

Excuse me @PierreBresson, could you please review the PR during the day? This is my last one in a Hacktoberfest-eligible repo, I hope I'll get the 4 PRs I need for the shirt...

[PierreBresson]

@a2br I've reassigned you to the task so you can get the t-shirt 👍 Merci beaucoup 👏

[a2br]

Mange tak, and happy Halloween! 🎃

[PierreBresson]

@a2br j'allais oublier: envoie moi ton adresse par mail à contact @ nmf . earth si tu veux les stickers cf #225 😉