WikiStatsExtractor must sum references by URI

[sandroacoelho]

The pairCounts file has 3(three) columns as follow:

• Surface Form;
• URI
• Reference count

When I run ./run Indexer lookup_index_dir redirects_en.ttl pairCounts, DBpedia Lookup must fill the index using URI as key, with all surface forms summing reference count.

Example:

Berlin http://dbpedia.org/resource/Berlin 33909
Europe/Berlin http://dbpedia.org/resource/Berlin 610

Reference count sum: 34519

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