Populate Wishlist with Unfulfilled Requests #296

As Donor Offers and Supplies are limited, Partner Requests can go unfulfilled sometimes, especially when there are multiple partners competing for it.

Currently, unfulfilled requests are just completely dropped. We want to change this so that all unfulfilled requests go into that partner's wishlist automatically. Here's an example scenario:

A Donor Offer is created, stating that there are 500 Bottles of Cough Syrup available. Three partners put in a request for this item:

• Partner 1 requests 200 with Low Priority, 0 get fulfilled
• Partner 2 requests 300 with High Priority, all 300 gets fulfilled
• Partner 3 requests 300 with Medium Priority, 200 gets fulfilled

In such a scenario, we want to automatically create a wishlist entry for Partner 1, with the quantity requested (200) and at what priority (low). We will also create an entry for Partner 3, with quantity unfulfilled from initial request: initial (300) - fulfilled (200) = unfulfilled (100). No wishlist entries are created for Partner 2.

Since wishlist entries allow for comments, any entry generated automatically should have the comment "Automatically generated due to unfulfilled request".

Throughly test this by creating various partner requests and various fulfillment splits.