Demo Changes

These changes are result of driving geotrellis-spark on a cluster to provide demos for presentations. They include some optimizations and a lot of bug fixes.

Most notably geotrellis-spark now does not have a hard dependency on spark and user must use spark-submit to launch it. This makes it a lot easier for geotrellis-spark to be used a library as spark-submit takes care of shipping JARs around.

Also note that Catalog now saves the raster histogram. This allows us to pain each tile with globally appropriate colors.
At some point we should probably structure the json formatters in a better way then having them all in this package object...not sure what's the best method, and not saying this has to change now, just putting the comment out there for the future.