GEOMESA-518,519 Refactoring of RasterIndexEntry and added Test

* RasterIndexEntry now properly encodes and decodes id, geom, time into the CQ of the key
* Added unittests for RasterIndexEntry, testing time optionally.
* Added new GeometryDecoder for decoding geometry from the CQ.
* Now using context bounds for some decoders, reduced some code duplication between IndexEntry and RasterIndexEntry.