Several updates to concrete-factorie

* Moved namespace to edu.jhu.hlt.concrete.converters.factorie to clean our the edu.jhu.hlt.concrete namespace
* Updated the pom to use new (stable/release) version of concrete and factorie
* Moved Tan's Concrete2Factorie method into the implicits object and formulated it as an implicit conversion
* Changed the conversions to use the JavaConverters format (ie. asDocument and asCommunication methods)