Add sentiment attributes to XML output

The following changes are included:

* Update XmlOutputter for sentiment: this allows us to use sentiment in the default pipeline
** Add a "sentiment" attribute to each sentence node for the 
** Add an "averageSentiment" attribute to the sentences node 

* Fix static method call in MorphaAnnotator -- just a quick fix from an IDE complaint

* Add sentiment to the default Stanford CoreNLP pipeline classpath properties