Merge lastest

1) moved add2HeuristicNounTable() to DataHolder class, added a utility method getWordPOSIterator to DataHolder class
2) Bug fix
3) Remove Setnence class. Use Token class instead
4) UnsupervisedLearningTokenzier -> OpenNLPTokenizer, UnsupervisedLearningSentenceDetector -> OpenNLPSentencesTokeinzer class
5) Some code clean up
6) Moved all data holder related classes to dataholder package
7) Added a missing method resetCounts() to Learner class