Bug 29987: Improve validation

Bug 29987: Improve validation

This patch adds hinting to display the required state of the cash
register fields.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit bce51debc65acfb89232a8603abb3e37c4f3b101)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 74406fdefd46e6a3c8e9fd18d6a119b913ecdb58)
Signed-off-by: Arthur Suzuki <arthur.suzuki@biblibre.com>