GEOMESA-277 Refining DensityIterator Stacking

* Refactored the DensityIterator to be separate from the SFFI.
* Moved the DensityIterator to run after the SFFI.
added tests for SVIngest, test files, and major refactoring of SVIngest to be better at errors.
finished writing tests for SVIngest, added more example files, added dispose call at finally in svingest
Merge remote-tracking branch 'lt/accumulo1.5.x/1.x' into fcr_majorly_improved_ingest_tool