Bug 26922: Better error handling in SendAlerts

Bug 26922: Better error handling in SendAlerts

This patch makes SendAlerts display a better error message when sending
fails.

To test:
1. Set KohaAdminEmailAddress to admin@example.org
2. Edit a vendor, set a valid email address
3. Create a new basket, a new order. Send the basket
=> FAIL: As you did not configure a valid SMTP server, the email is not sent and logs displayed "unable to establish SMTP connection to (localhost) port 25", with the stracktrace.
4. Apply this patch and reload all
5. Repeat 3
=> SUCCESS: A simpler message is displayed, the stacktrace remains in
the logs
6. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>