Automatically kick users if they don't change their username

[TimJentzsch]

To help keep the server clean and deter bots, we kick a user after 12 hours if they haven't adjusted their nickname to the desired format.

Buttercup should do this automatically, tracking users that have an invalid nickname and kick them after the time expires.
Before it executes the kick, it should check again that the display name is still invalid, to make sure that users aren't kicked when their name is correct.