Bug 29746: Add Koha::Result::Boolean

Bug 29746: Add Koha::Result::Boolean

This patch introduces a new OO class that can be used as return value
from methods that need to return boolean values, but also provide some
feedback. This last bit is implemented using Koha::Object::Message
objects that can carry valuable information.

This class can also implement a `to_api()` method so it is suitable for
API usage. And so the Koha::Object::Message class. Will be done as
needed.

If some other result types are required, then we can move some of the
messaging logic to a top-level Koha::Result class this one inherits from
(and the new one as well, say, Integer?).

To test:
1. Apply this patchset
2. Run:
   $ kshell
  k$ prove t/Koha/Result/Boolean.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>