Improve (functional) data management sequence

[hmgaudecker]

This might be one of the most important topics we have, at least the most impactful because factually everyone is using it.

I think the sequence should be changed such that we have

1. Introduction of the example
2. Show typical imperative way (people may or may not want to watch that)
3. Functional: Basics (fundamental rules + simple application)
4. Functional: Advanced. This would include a discussion of trade-offs (e.g., when to write things out as in the simple example / when to use loops, potentially over metadata).

Beyond that, we should change the "rules" lecture so that it is partly included in 3./4. and the rest is more about "rules for complex data" (normal forms etc.), which would come after the functional and merging bits.