Bug 28627: Calculate unitprice if not set

Bug 28627: Calculate unitprice if not set

On bug 23376 the developer was too clever by half. Instead of passing
values to the template we moved to simply passing the order object.

The calculations that populated the unitprice, however, were simply dropped.

This patch restores the behaviour of setting unitprice to the estimated cost
by default. We do this conditionally in the template

To test:
 1 - Create a basket and adding items to it. Set the 'Vendor price' to
    '20', do not add an 'Actual cost'
 2 - Close the basket
 3 - Select 'Receive shipment'
 4 - Set a value for vendor invoice
 5 - Receive the order you created
 6 - Observe 'Actual cost' is = 0.00
 7 - Apply patch
 8 - Refresh the order receival page, and confirm the 'Actual cost' =
    20.00
 9 - Cancel receipt - reopen basket - edit order - add an actual cost - close
10 - Receive the order again
11 - Confirm the actual price is used
12 - Repeat this whole plan, but ensure the vendor has a different value for
     Invoice prices: Include tax

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>