"message_class" contains the string "info" / "success" / "warning" / "error",
where "class" contains the bootstrap CSS name.

This caused template failures, meaning people could not see what
they did wrong. How the field is called is now abstracted away
by using kwargs instead of a dict.

This simply happens, as users are being users. It is not a log
message that is useful for anyone, except when developing. In that
case you get this nice page telling you the project doesn't exist.