Refactors to geotrellis-spark

This PR modifies the geotrellis-spark API to
 - remove type aliases to tuples where case classes produces cleaner code
   - TileIdRaster is now Tile
   - TileIdCoordRaster was refactored out, the tile coords can be found on the Tile
 - Makes RasterHadoopRDD private, creation of RasterRDD directly by client.
 - Moves from a Object.toOtherType(instance, ...) to instance.toOtherType(...) pattern, which is more in line with the rest of the library.