Make configuration less opaque

[yfcai]

Configuration lives in an undocumented private repo. I remember how to link to it now, but I won't remember forever. To fix it:

1. Make the private repo a submodule.
2. Add sample configuration files.

[phischu]

Dear Cai,
I am reactivating the tutorial assignment and noticed that a scheduler-secret folder is missing. It would be nice if you could send it to my philipp.schuster at uni tuebingen email. If you find the time.