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

heh... I first tried

scala> val m:Int = null
<console>:7: error: an expression of type Null is ineligible for implicit conversion
       val m:Int = null
                   ^