Added latest strings to de-DE and a diffchecker

[LauraWebdev]

I've just added all missing strings to de-DE.

The second commit is a small diff checker script for locales that shows which strings changed and which are new. Very useful to quickly see which strings need to be added (previously it was a real PITA to look through both files to check the differences).

Usage: npm run locale:diff -- de-DE

[samuelmaddock]

Thanks for adding the script, looks useful!

A couple of requests before merging:

• Move script from metastream-app/localeDiff.js to metastream-app/scripts/localeDiff.js
• Remove package-lock.json and install using yarn instead of npm

[LauraWebdev]

I've pushed a few commits for your requests

[samuelmaddock]

Thanks for making those changes. 🙇