Deal with QUERY_OVER_LIMIT response from google

This is currently deployed on webdev.  I successfully geocoded 100 in one go (something that failed previously because requests were being submitted too rapidly).  If someone else wants to test, I think this is ready to ship.

Note that there's a limited number of requests that can be submitted in a 24 hour period, so if you're going to test, please test with something like 100 or 200 geocoding attempts.  Also note that there is a 2-second wait if a geocoding attempt comes back with a QUERY_OVER_LIMIT response, so if you're doing 200 at a time, it *could* take 500 seconds (although it probably won't)

Fixes #585