Ability to georegion code based on a string

This enables directly georegion coding against a column containing zip code strings (eg. "98122") instead of having to geocode the zip code to an additional point column and then georegion coding that column against the region polygon.
The conflict isn't happening between the spatial cache instance and the map cache instance - the metric name is already prefixed with the class name eg. com.socrata.geospace.regioncache.MapRegionCache.num-entries . The conflict is happening in unit tests when 2 different tests instantiate a cache of the same type.

I am pretty sure the issue is in the scala-metrics library. If you look at `nl.grons.metrics.scala.MetricBuilder`, the `gauge` method calls Codahale's `registry.register` (which throws an exception if a metric with the same name already exists), while the other methods like `timer` call Codahale's `registry.timer` (for eg) which in turn calls `getOrAdd` - as the name suggests, that method doesn't throw if the metric already exists.