Tickets have many Comments.

Comments is a SortedSet based on Timestamp.

Removed closingComment and detailedDescription, because really I think a
slick GitHub like interface where a Close & Comment button would be
nicer, lending to the Comments being more uniform.

The Comments relationship requires a minimum of 1, implying the first
comment is the description.
isClosed implied by dateClosed.

Unless there is need for a "soft-close" system, or for allowing Tickets
to be re-opened, dateClosed not being null is sufficient for determining
if the Ticket is closed or not.