Update Geospace handler to expect numeric georegion feature IDs

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.
Why are we doing double Some's?   What value does this serve?

If the base Option[T] is oK, then I don't see why we can't just use rojoma-json's built in Option parsing.