Bug 38013: Add classes to messages in returns.tt

Bug 38013: Add classes to messages in returns.tt

To test:
1 - enable FineNotifyAtCheckin
2 - enable AllowCheckoutNotes
3 - check out an item to a patron with fines on their account
4 - check out an item and place a checkout note on it
5 - check each item in, confirm each produces a message with the classes alert, alert-info, and alert-warning
6 - apply patch, restart_all
7 - repeat steps 3 and 4
8 - check items in, confirm messages now include issue-note and patron-fines classes

Signed-off-by: Brendan Lawlor <blawlor@clamsnet.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>