Added Sentiment Analysis Graph Property Worker

(Sentiment Analysis is from Stanford's CoreNLP library)
Changed pom files & lumify.properties file.

Please add:
ontology.iri.sentiment=http://lumify.io/dev#sentiment
to your lumify.properties file.

The sentiment value is represented with a number between -1 and 1, with -1 being very negative, 1 being very positive, and 0 being neutral. Sentiment analysis works on any extracted text. See example image below:


![sentiment analysis](https://cloud.githubusercontent.com/assets/7842395/3882594/8c75b094-2198-11e4-83f6-8c358022b388.png)