Bug 27583: Proposed terminology changes

Bug 27583: Proposed terminology changes

This patch impliments some terminology changes and clarifications for
the cash management system

Test plan
1/ Apply the patches
2/ Enable 'UseCashRegisters'
3/ Navigate around the cash management system (via the Tools menu)
4/ Enable 'EnablePointOfSale'
5/ Navigate around the cash management system (via the Point of sale
module)
6/ Comment on what you think about the changes

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>