Re-Review yaml-model extension

For some seemingly inexplicable reasons, the old merge caused the crawler to not being able to parse table values correctly anymore (see, e.g., https://gitlab.indiscale.com/caosdb/src/caosdb-advanced-user-tools/-/jobs/87361#L207). We have to find out what was the problem and fix it first. Also, the parser error looked as if they should be unit-testable.

• If possible: unittest written
• Found problem with parser
• Fixed and integration tests run again