This patch allows to resend both sent and failed messages.

With messages in 'sent' status, we have to be careful not to accidentally send
sent messages again. With the previous patch using GET request, this was likely
to happen because of browser storing the GET parameters.

This patch changes request method from GET to POST. Instead of a simple link,
we now have a form element.

In notices.pl we redirect back to notices.pl, because with POST there is a risk
of resending the message accidentally by form resubmission at refresh.

To test, find/create a Patron that has sent or 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 sent or failed message
4. Observe that there is nothing for resending the sent or failed message
5. Apply the patches.
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

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