Make InfoboxExtractor work

This solves #50 to the point @jimkont and I discussed (the extractor will work, only a few Quads with duplicate propertyUri will remain - note that these are not totally duplicate Quads). And also the related #52 .

Dimitris - I didn't need to add an extra property or skip the HashSet duplicate checking. This will simply filter duplicates in each worker as usual (I kept it as is because it isn't hurting execution), InfoboxExtractor doesn't care about the bigger picture, so allover we'll still have duplicates.

@jimkont @sangv please review and merge this? If needed we can have a quick Skype chat. Ask me if you need any clarifications.