Bug 36098: Add Koha::Session module to ease session handling

Bug 36098: Add Koha::Session module to ease session handling

This patch adds a Koha::Session module that makes it easier
to work with Koha sessions without needing the full C4::Auth module.

Test plan:
0. Apply the patch
1. Run the following unit tests:
prove ./t/db_dependent/Auth.t
prove ./t/db_dependent/Auth_with_cas.t
prove ./t/db_dependent/Koha/Session.t
2. Observe that they all pass

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 0e6537d199fe49a9e91e1c75f9462ddf1c878fed)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>