Bug 26273: (follow-up) Add 'Cashier' to the cashups table

Bug 26273: (follow-up) Add 'Cashier' to the cashups table

This patch adds the 'Cashier' field as discussed on the bug report.

Test plan
1/ Apply patch and reload the register page to refresh the table
2/ Note that a 'Cashier' field now appears in the table
3/ Sorting and searching on 'Cashier' should work as expected
4/ Default sorting should remain as 'Date' order.
5/ Signoff

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Bug 26273: (QA follow-up) Check for null firstname

This patch adds a test for firstname being defined before constructing
fullname from it.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>