Added sql file to make the bans table better

This MR is part of a larger project I picked up in which I am planning to make the database somewhat better, introducing stricter relationships between tables, more logic data types (i.e. tinyint instead of strings for flags) and a lot more.

This MR adds a breaking change, since the (unreadable) integers in the bans table are changed to datetime columns. All CMS's count on the former data type, so they need to be changed to the latter in order to get this change to work.