IndexIterator Work-in-progress

A work in progress branch to address GEOMESA-101 --- adds an IndexIterator that can be used in place of the SpatioTemporalIntersectingIterator. 

This PR is for comments. I'd still like to write a few unit tests for the indexIterator's trigger logic as well as remove the use of JavaConversions.

replaced with .getOrElse(sourceSimpleFeatureType).