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

Something similar is defined in geomesa-core/src/main/scala/org/locationtech/geomesa/core/data/package.scala

If it makes sense, it might help a little.