Improved error message for faulty row tokenisation

Users encounter errors such as:

```
[...] skipped row 59213 b/c does not have a proper <isa> statement or is missing required attributes. Faulty tokenized row: [...]
```

However, it is unclear exactly which part of the row is faulty. If the issue is a required attribute is missing, we should be able to print out the column number/name that is required but missing.