Load google maps js should be optional

[ar-anvd]

Otherwise you can get this error. In my case I am using google api in another pages (base template) that leads to a duplicate import.

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

https://github.com/rochacbruno/Flask-GoogleMaps/blob/9162e563bc4af78ee1235967487beffa5b061483/flask_googlemaps/templates/googlemaps/gmapjs.html#L3