Bug 15780: Add inventory number to checkout list on summary print

Bug 15780: Add inventory number to checkout list on summary print

This will add the inventory number to the list of checkouts that
can be printed using the 'Print summary' feature from the patron
account in staff.

To test:
- Apply patch
- Make sure you have some items with and without inventory number set
- Check them out to any patron
- Go to Print > Print summary
- Verify the inventory number column is showing up and the numbers
  show with their items.

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>