Bug 24541: Purge old messages

Bug 24541: Purge old messages

misc/cronjobs/cleanup_database.pl provides some database cleanup.

This patch adds cleanup for messages table.

Test plan :
- Count messages : select count(*),date(message_date) from  messages group by date(message_date);
- Run cleanup : misc/cronjobs/cleanup_database.pl -v --confirm --messages 365
- Recount messages

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>