GEOMESA-169 fixing density iterator, restoring expansion of density map

There is still more work to be done on 169 to fix some artifacts in certain queries, but this is a first step that restores the expansion of features and fixes iterating over the sub-iterator and compiling the results.
I'd push for factoring out data creation in order to re-use the points elsewhere.  

Also, we can create points, throw them in a MockDataStore and then query a few times.