clean up of spark test fixture
removing SharedSparkContext trait
extracting RasterMatchers to testkit, they work on Tiles
add: EmptyTile is a ConstantTile with a type marker
RasterRDD[SpatialKey] can be translated to CompositeTile as a form of collect
gitignore test-catalog
test-catalog will now generate itself if not present
matchers will report col/row of error, so useful
unnecessary companion objects are unnecessary
don't lie about the return type, life is hard as is
more clear comment
fix: tile count bug in generating test files