Add a basic ingest and export utility to get geotiffs in/out of geotrellis-spark

This adds a basic Ingest and Export utility to get geotiffs in/out of geotrellis-spark. The goal is to have a simple and fast way to get data in/out so we can start building operations for manipulating rasters on Spark. Ingest is currently single-threaded and holds all tiles in RAM. Export uses RasterHadoopRDD to read tiles out. 

Overview of changes:
1. Renamed "Image" to "Raster" throughout the geotrellis-spark codebase to make it consistent with the rest of geotrellis. So ImageHadoopRDD is now called RasterHadoopRDD. 
2. Added PyramidMetadata, a JSON backed class for encapsulating all metadata related to the raster. 
3. Added sumac 3rd party library for command line parsing 
4. Added Ingest and Export top-level applications