Switch Babel dependency to YAML file for tutorials

[TiBiBa]

Description In this PR we switch the tutorial translations from Babel to a YAML file to better enable us to add new levels and steps without losing the overview. We cache all tutorial language / keyword language combinations on server start to reduce server load and enable dynamic keywords. Currently this is not relevant, but probably will be when adding the tutorials for new levels.

Fixes This PR fixes #3165.

How to test As this is a re-structuring task all should work as before. To verify log in and navigate to /tutorial, verify that all steps stil work as expected.