Added a DBPedia search engine

I needed to change the result structure a little bit, but the DBPedia class now provides a gateway for sparql queries against DBPedia. If this is interesting to the project, I have also considered some other tools namely a freebase connector and a MongoDB connector.

Here is an example usage of the dbpedia code:
```
#  Some Usage Examples:
# >>> from pattern.web import DBPedia
# >>> DBPedia().search('select distinct ?Concept where {[] a ?Concept}')
# >>>
# >>> results = DBPedia().search('PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX : <http://dbpedia.org/resource/> select * where {?a rdf:type ?s.}',"SPARQL", 1,1)
# >>> for row in results:
# ...   print "Entity: " + row.data('a') + " ( " + row.data('s') + " )"
# ...   print row.download('a')  
```

Thanks,
- Ken