Urls taken from config instead of hardcoded

Urls are loaded from the configuration instead of being hardcoded.

Note the example values in `server.py.dist` use trailing slashes on the index urls, which must be retained by the user values. The use of trailing slashes in `server.py.dist` is inconsistent and may want revision in the future (eg `WWW_DOCUMENT_ROOT` vs `API_INDEX_URL`).