for comments - GEOMESA-233 adding scalding job to index attributes through geoserver UI

Still TODO - 
* create ticket for the TODO in the code
* error handling in UI for failed m/r jobs
* unit tests

scala> null
res7: Null = null
scala> res7.asInstanceOf[Int]
res8: Int = 0

Ok, I was wrong.  That said, null.asInstanceOf[T] can do weird things.