New module elasticsearch, new pom, new classes

Adds a new module called elasticsearch to dbpedia-spotlight project.
This module will be responsible for upgrading the indexing task to
use a newer version of the Apache Lucene framework. Also adds two
packages, index.elasticsearch and util to this module.

Adds the base classes (initial code only) to the index.elasticsearch
package to read input files and wrap around the ElasticSearch Java
API.
  - Adds the class ElasticCandidateSearcher.scala
  - Adds the class ElasticCandidateIndexer.scala
  - Adds the class ElasticContextIndexer.scala
  - Adds the class ElasticContextSearcher.scala
  - Adds the class ElasticParagraphDisambiguator.scala
  - Adds the class ElasticSearchIndexer.scala

Adds the base classes (initial code only) to the util package.
  - Reuses the IndexingConfiguration.scala class from the lucene.index
  package in the index module. This class loads the configuration file
  and can retrieve information in the properties file.
  - Reuses one class and a trait from the db package in the index
  module used to read pig token files:
    . TokenOccurrenceParser.scala (trait)
    . TokenOccurrenceParser.scala (class)

Adds a new pom.xml to the new module with basic configuration. It is
not possible to call the classes using -Dlauncher at this moment.