Bug 18403: Refactor and add Koha::Patron->libraries_where_can_see_patrons

Bug 18403: Refactor and add Koha::Patron->libraries_where_can_see_patrons

Technical note:
Here we are just refactoring a code that have been copied into 3 different places.
libraries_where_can_see_patrons is a terrible method's name, feel free to suggest
something better. The method return a list of branchcodes to be more efficient,
instead of Koha::Libraries

Signed-off-by: Signed-off-by: Jon McGowan <jon.mcgowan@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>