Bug 13972: Include fields from subscription and serial table in serial notification...

Bug 13972: Include fields from subscription and serial table in serial notification email

Currently it's not possible to include information about which
issue has arrived in the serial notification notice the patron
can subscribe to from the OPAC.

The patch makes the fields from the subscription and serial
table available to the notice template.

In order to be able to print information about the correct
issue, the GetAlert has been modified to expext the serialid
as externalid when the module is issue.

git grep SendAlerts (only call with 'issue' is in Serial.pm)

To test:
- Add a subscription, select a patron notification template
- Search for the record in the OPAC
- Go to the subscription tab - More details
- Subscribe to the notification
- Edit the notice template you selected for the subscription
  - add fields from subscription
  - add fields from serial (serial.serialseq has the issue
    information)
- Receive an issue for the subscription
- Check that you have received the notification and that
  all information has been printed correctly
  NOTE: notice is sent directly, not through the message_queue

Followed test plan, works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>