Letters / alert system, continuing...

Letters / alert system, continuing...
* adding a package Letters.pm, that manages Letters & alerts.
* adding feature : it's now possible to define a "letter" for any subscription created. If a letter is defined, users in OPAC can put an alert on the subscription. When an issue is marked "arrived", all users in the alert will recieve a mail (as defined in the "letter"). This last part (= send the mail) is not yet developped. (Should be done this week)
* adding feature : it's now possible to "put to an alert" in OPAC, for any serial subscription. The alert is stored in a new table, called alert. An alert can be put only if the librarian has activated them in subscription (and they activate it just by choosing a "letter" to sent to borrowers on new issues)
* adding feature : librarian can see in borrower detail which alerts they have put, and a user can see in opac-detail which alert they have put too.
Note that the system should be generic enough to manage any type of alert.
I plan to extend it soon to virtual shelves : a borrower will be able to put an alert on a virtual shelf, to be warned when something is changed in the virtual shelf (mail being sent once a day by cron, or manually by the shelf owner. Anyway, a mail won't be sent on every change, users would be spammed by Koha ;-) )