Revert "Remove unused ruamel.yaml dependency"
Revert "Remove unused ruamel.yaml dependency"

On second thought, it's not unused.

This reverts commit 7f1cdc1403d95ca0cb77b4f544d130c6c04c145a.

amcat/amcat,amcat/amcat,amcat/amcat,amcat/amcat,amcat/amcat,amcat/amcat