Improving error message when using the outdated csv format

[staudtMarius]

Resolves #1112

[sebastian-peter]

The existing error message (The size of the headline does not fit to the size of the resulting fields to attributes mapping.) could also be made more clear. I'd remove the print of fieldsToAttributesKeySet, since it's just going to be headline with a maximum size of the length of fieldVals.

Please also make sure that there are tests for both cases: Too many and too little headline fields.

[sebastian-peter]

Looking into this again, we might introduce a new bug here if there are multiple headlines with the same (or similar, since they're case-insensitive) names. So it might have been good the way it's been before.

What for sure needs to be fixed is line 172 in the original CsvDataSource, since the headlines array might be shorter than the fieldVals array. Let me prepare my proposal.

[sebastian-peter]

Well that escalated quickly.
Additional chanegs:

• CSV row parsing now throws SourceException
• Duplicate headline detection
• Adapted test grid format, which was outdated but no-one noticed because exceptions were not thrown

[sebastian-peter]

@staudtMarius gave his ok to my changes, merging :)