Use a numeric feature ID instead of directly copying the string ID from the shapefile

N.B. Please leave merging the branch to me (Urmila) - without running the appropriate migration script immediately afterwards (which I am still working on), staging will be broken.
Yeah, I started out that route, but it just got super messy to pass consistent IDs around from FeatureIngester to the servlet and then back out to the RegionCache. This actually ended up being a much cleaner way.