Periodically reload maps from server as we add to them.

It takes 30 seconds for the summary data to be rewritten for a grid. Also, we have caching on the client. So it isn't clear when we would actually see new data on the server. We should make sure to b reloading every minute as we're sampling - no need to overwhelm the server or communication link, but we do want to know that transmissions are arriving when they do.