Add back SystemGeometries

Supersedes #349 (has an additional commit added to address a bug with tests). After this is merged, make sure to either reprovision or update geotrellis and publish-local -- https://github.com/geotrellis/geotrellis/pull/914 has been merged which provides a dramatic performance enhancement when generating the geometries.
Generally, I'm a fan of the '->' syntax for Maps. I think it makes it clearer when you're potentially dealing with tuples.