Add error-log interface

[Luzifer]

As an user having someone else host the bot for me I don't have access to the CLI logs of the bot and therefore cannot see which errors occurred when adding new rules or executing commands with unexpected results.

In order to improve this the bot should have an interface any authorized user can use to see the bot logs. To make this possible the logging (>= info level) should be written into a table with a sane default retention (30d?) and auto-cleanup of that table. An interface should be available to query information from that table.

This also would make the log actor way more useful as the logs can be seen without access to the server itself.