GEOMESA-234 using lexicoders for secondary index values

* Using mango lexicoders for primitive types
* Moving some encoding/decoding logic into more consistent locations
* Updating attribute strategies for querying with lexicoders
Yes, go ahead.  The DensityIterator stacks on additional mojo, but only in the StIdxStrategy.  

Can you also add a ticket about using the DensityIterator work with non-stidx strategies?  I think this may get into meta-strategies.  In general, this also gives us a chance to think about extracting the Density (more general analysis iterators) logic from a particular place in the query planning.

That said, I don't see that being easy.