Add geocoding rate limiting

[alulsh]

The Mapbox Geocoding API has a rate limit of 600 requests per minute. Currently, if you load a large enough family tree you may hit the rate limit and receive an error in the browser console. We should make this error message more user friendly via a modal.

We should also implement a client-side library like https://github.com/jhurliman/node-rate-limiter to help throttle API requests and prevent rate limit errors from happening in the first place.