AID-749 Added more logging using base class.

- Added logstash setup to config/config-example.yml.
- Added config/site-example.rb, to be removed later when AID-750 is done.
- Removed custom logging setup no longer needed.
- Replaced halt with abort from base class to log failures.
- Added more detailed logging for login success/failure.

May not be a `username` either, as we support loggin in through `token`. But we could add the username if it is present, I guess. But I'd like to avoid branching code just for logging.