This patch adds a link 'Resend' under a notice in 'failed' status
in the Patron's Notices tab.

By clicking the link, we will request notices.pl with parameter
"resendnotice=XXXXX" where XXXXX is message_id. In notices.pl,
we then check whether the given message is actually in 'failed'
status. If so, we use the C4::Letters::ResendMessage(123) to
change the status of the message into 'pending'. This way it
will be processed again by the cronjob process_message_queue.pl.

To test, find/create a Patron that has failed notices in message_queue:
1. Enable EnchancedMessagingPreferences system preference
2. Go to Patrons -> Notices
3. In the Notice column, click the title of the failed message
4. Observe that there is nothing for resending the failed message
5. Apply patch.
6. Reload Notices page and repeat step 3
7. Observe that there is now a link "Resend" in the Status-column
8. Click Resend
9. Observe that the message gets into 'pending' status

Works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>