Allow user to turn off googleapi call

[dcooley]

Sometimes it's useful for the user to include their own <script src="https://maps.googleapis.com/maps/api/js?key=%s&libraries=places&callback=SomeCallback" async defer></script> call, with their own SomeCallback() function

so we should be able to turn off the api call from within google_map()

(to prevent the API being called twice:)

You have included the Google Maps JavaScript API multiple times on this page. This may cause unexpected errors.