Renamed TileIdRaster to Tile, refactoring out type aliases.
Fixed tests.
Removed additional type aliases, more refactors.
Removed withContext package method; use mapTiles & combineTiles
Made RasterHadoopRDD private to geotrellis.spark.rdd

Created apply on RasterRDD for loading from RasterHadoopRDD.
Removed dupe import
Merge pull request #749 from lossyrob/spark/localoperations

Refactors to geotrellis-spark
Merging in upstream