Mapbox data as environment config

[manumoreira]

Small suggestion, maybe not worth the effort: it'd be ideal if these values came from the environment configuration. The mechanism we have right now is:

define the variables in the application configuration with values from the environment, as in https://github.com/instedd/planwise/blob/master/resources/planwise/config.edn#L157 or https://github.com/instedd/planwise/blob/master/resources/planwise/config.edn#L99
add the values to the rendered client configuration in the home endpoint, by extracting the values from the Duct configuration map (eg. https://github.com/instedd/planwise/blob/master/src/planwise/endpoint/home.clj#L34). This will result in the values being rendered in the global JS variables _CONFIG
implement a couple of vars in the client's config namespace: https://github.com/instedd/planwise/blob/master/client/src/planwise/client/config.cljs#L14
use the vars from such namespace, as in https://github.com/instedd/planwise/blob/master/client/src/planwise/client/design/views.cljs#L139
This way we can define the map ID and access tokens as environment variables in the deployments and if they change we don't need to rebuild the Docker image.

Suggestions copied from #614 review