Package alterator-squidmill: Information

- Display `squidmill` command error message (last line) if any.
- Make the initial backend query async.

- Require alterator-service-functions >= 2.0.2.
- Do not redirect the query log for the purpose of debug.
- Write the report to disk. Always return 0 to the message handler.
- Fix: select unique users (TODO: add the special query to squidmill).
- Fix/improve the error handling.

- Check both the 'enabled' and the 'active' status values of
  the service.
- Require squidmill >= 2.4.
- Include more log lines in the error message.
- Try socket first of direct DB access.