GEOMESA-537 Add raster query

There are existing encoders and decoders for time and bbox in joda and in geotools.  Why do we need custom encoders here?  Also, AccTimestamp - that sounds like we're using the timestamp element of the Accumulo key 5-tuple to persist the value at that time.  I think using the timestamp element of the tuple is not a good idea - we have run into issues with that elsewhere.