Better managment of backend's backend API calls

[ttben]

To fix #72 , we must ensure that the actual backend's backend API is called only in integration and production mode, drastically limiting the number of calls.

In addition, client-caching strategies can be added to avoid unecessary call to our backend, but as long as the backend does NOT trigger an data API call each and every time, we should be fine.

[rte-opendata]

Please, see issue #74