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.

Possible to add `user_id` to the log message?

And context, if it's not already there?