Format-specific parts of replies, including the role name and
attachments, are now stored in separate columns. This allows us to
store only one version of the actual message body and, by keeping
format-specific data separate, reproduce formatter results regardless
of when they are called. This cleans up code around message formats
significantly and was required to support !edit/!delete properly.
A thread can be scheduled to be closed by adding a time parameter to
the !close command. For example, !close 2m would automatically close
the thread in 2 minutes. The actual scheduling is implemented with a
loop that runs every 2 seconds, checking for threads that should be
closed.