Remove usage of scala.util.parsing.json.JSON (deprecated in scala-2.11)
Changed JSON to PropVal conversion to create Vectors for array data

JsArray from parsed JSON string contains a mutable ListBuffers instead
of an immutable Seq type, so we need to convert to something immutable.
Updated build to scala-2.11.2, akka-2.3.6 and sbt-0.13.5

Also updated version of other dependencies
Changes for scala-2.11 compatibility
Adapted code to akka-2.3 deprecations