Prototype for distributed extraction using Spark

OK, so this is directly from my old repo at https://github.com/nilesh-c/dbpedia-dist-extraction with a few unneeded files removed.

1. Shall I remove the submodule?
2. A lot of changes need to be made here though. eg. line 106 of dist/src/main/scala/org/dbpedia/extraction/dump/extract/DistConfigLoader.scala - hardcoded SPARK_HOME. Need to take it from Config.