Bug 16497: (follow-up) Adapt to existing guidelines and RFC

Bug 16497: (follow-up) Adapt to existing guidelines and RFC

This patch makes the original implementation match what is specified on
the RFC [1].

The controller is updated, and so the tests.

To test:
- Apply this patches:
- Run:
  $ kshell
 k$ prove t/db_dependent/api/v1/libraries.t
=> SUCCESS: Tests pass!

[1] https://wiki.koha-community.org/wiki/Libraries_endpoint_RFC

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>