Bug 29695: Add new module Koha::Database::Columns

Bug 29695: Add new module Koha::Database::Columns

This module will contain new strings and make them translatable using
Koha::I18N.

We will need to improve this module to prevent the dozens of __ calls
each time we retrieve the column list. We could either use memcached or
add a method to only retrieve columns for a given table.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>