Bug 23916: (follow-up) Fix terminology, use patron-title and make column consistent...

Bug 23916: (follow-up) Fix terminology, use patron-title and make column consistent in issues and old_issues

This commit makes the changes suggested by Katrin in comment #50:

- Changed syspref from RecordIssuer to RecordStaffUserOnCheckout
- Changed terminology from "issue" to "check out" and variations
- Fixed name display to use patron-title.inc
- Made issuer column DEFAULT NULL consistently between issues and
old_issues and between the DB update and kohastructure.sql

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>