Retrieve list of cooperatives from an API instead of reading official website

[alexsegura]

The list of cooperatives (i.e cities) showing when the app first loads is retrieved from the official website.

This will soon be deprecated. Instead this list should be retrieve from a shared API (to be defined).

To avoid too much coupling between the API & our infra, the API URL could look like:

https://api.coopcycle.org/app/cities

The list could then be filtered by country, for example:

https://api.coopcycle.org/app/cities?country=fr