Bug 31389: Calculate user permissions in separate function

Bug 31389: Calculate user permissions in separate function

This patch refactors the setting of user permissions for templates into
a new function, which can be easily unit tested and reduces the amount
of code in C4::Auth::get_template_and_user(). It also aids in the
re-usability of permission checking code.

Test plan:
0) Apply patch and koha-plack --restart kohadev
1) prove t/Koha/Auth/Permissions.t
2) As koha superlibrarian, go to
http://localhost:8081/cgi-bin/koha/tools/tools-home.pl
3) Go to http://localhost:8081/cgi-bin/koha/members/members-home.pl
4) Create new test user with "Staff access..." and "Remaining circulation permissions"
5) Logout of koha superlibrarian
6) Login as test user
7) Note you can only see a limited view of the staff interface
(i.e. no administration, no tools, no reports, etc.)

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>