GEOMESA-558,571 RFI integration and improved RasterStoreTest

* RasterQuery now takes resolution as a double
* RasterFilteringIterator now wired in, with tests
* Noted geohash enumeration issue in one of the tests
* Made RasterTestUtils for common functions in the tests for geomesa-raster
* Improved RasterStoreTest
Maybe also move the code from geomesa-plugin/src/test/scala/org.locationtech.geomesa.plugin/wcs/GeoMesaCoverageReaderTest into here. I think it fits better here anyway.