Bug 33039: Add ability to specify a template for serial subscription "Published on...

Bug 33039: Add ability to specify a template for serial subscription "Published on (text)" field

Some libraries would like to have the text version of the serials
"published on" field auto-generated from a template. This template
should be definable at the subscription level.

Test Plan:
1) Apply this patch
2) Run updatedatabase.pl
3) Restart all the things!
4) Create or edit a new subscription
5) Edit the "Publication date template", create a template toolkit
   template.
   Keys available are the Koha::Subscription object as 'subscription'
   and the following serial table columns as keys:
    serialseq
    serialseq_x
    serialseq_y
    serialseq_z
    subscriptionid
    biblionumber
    status
    planneddate
    publisheddate
    publisheddateext
    notes
    routingnotes
   So your example template could be "[% subscription.subscriptionid %] [% biblionumber %]"
6) Generate the next serial
7) Note the next issue has a "Date published (text)" field based on the
   template you set!

Signed-off-by: Laura Escamilla <laura.escamilla@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>