GEOMESA-228 Remove unstable tests

* Removed tests in FilterTester.scala from the build.
 Those tests were failing in somewhat arbitrary and non-reproducible ways.
GEOMESA-57 Adding default constructor for TimestampSetIterator and test (originally from @cne1x)
GEOMESA-209 - Identifying unique GeoHash sub-strings in a polygon is both slow and inaccurate

Added a few new unit tests, re-wrote the way we compute these
GeoHash sub-strings, and added a few utility methods to the
RectangleGeoHashIterator and the GeoHash.
GEOMESA-191 Implement deleteSchema for featureType

deleteSchema removes both metadata and the 3 tables per feature type. Also
checks to see whether or not it's an older 0.10.x table, and if so, uses
the AccumuloFeatureWriter's remove() function to remove rows from the table.
GEOMESA-231 Allow longs in SimpleFeatureTypes