New indexing

While updating the index to DBpedia 3.8, I made many changes along the way.

- index data coming from [pignlproc nerd-stats.pig](https://github.com/dbpedia-spotlight/pignlproc/blob/master/examples/nerd-stats/nerd-stats.pig) that provides surface forms and scores
- Indexer does not assume sorted input any more, but it speeds up the process
- default_index_path is not used any more (was a weird idea to begin with)
  give the index dir directly to the Server
- DEF dependency because we need WikiUtil and don't want to duplicate any more

**IMPORTANT**: added Apache License 2.0 file.