Proxy google maps api through the server

[jspaine]

At the moment the google maps keys are sent to the client so it can load the js api. This exposes the keys so it would be better to proxy requests to the google maps api through the server, which can add the keys to the requests and avoid exposing them.

It's also really confusing because we allow setting the api key through an environment variable which is only used to populate the db during seeding, while you'd expect it to be applied each time the server is started.