Alexei Quapp

@alexanderpann That's the one thing that fell under the table :/ I was ensured that it was already handled, but apparently not. I don't know the changes, but will review...

This PR was cleaned up and updated by #2402 and thus will be closed together with #2402.

Extended DataTableLookUp with an optional argument to specify a default row, so if no result is found and the column doesn't contain an empty value, the default row is returned.

The lastest changes look good and are working ([45b6c56](https://github.com/IETS3/iets3.opensource/pull/624/commits/45b6c5656ae3e8d2a4cfcead352a99d15268148c) + [02f1a08](https://github.com/IETS3/iets3.opensource/pull/624/commits/02f1a0837309653c799efcf16a30d999d88f6583)). This also resolves the initial limitation. Great Job!

**Question: Do we have an convention when to use `#alias#`-cell and when to use a simple constant-cell?** In this case the `lookUpBy` and `default` cells are `#alias#`, which means, they...

The `default`-part of the `DataTableLookUp` cannot be deleted, when the cursor is placed on the `default` keyword. Deleting from the `=` and from eg. first position of the value works...