GEOMESA-113 Change naming scheme to reflect Accumulo version
GEOMESA-109 Refactor IndexSchema

* Broke up the IndexSchema file into separate files.
* Changed the STII's use of an IndexSchema to a IndexEntryDecoder.
* Pushed everything down into the IndexQueryPlanner in preparation for work on it.
GEOMESA-111 Remove the AggregatingCombiner

* In order to remove the AggregatingCombiner, we needed a new 'Is this a data row?' signal.