Bug 36908: Sort branches based on branchcode

Bug 36908: Sort branches based on branchcode

This adds a sort based on branchcode, it's a fallback for an edge case that should be rare
so I think is acceptable, as long as documented.

I added test coverage, but it may no longer be possible to encounter this scenario.

System preference descriptions are updated as well.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>