Validate date ranges in Close Dates editor

Complain in Closed Dates Editor when ending date is earlier than starting date.

Signed-off-by: Pasi Kallinen <pasi.kallinen@pttk.fi>
Signed-off-by: Remington Steed <rjs7@calvin.edu>
Signed-off-by: Ben Shum <bshum@biblio.org>