Bug 17515: Order Z3950 server by rank and preserve ordering

Bug 17515: Order Z3950 server by rank and preserve ordering

Previously we put all the servers into an object with keys of the server id

This patch converts it to an array of objects to preserve order, and adjusts code to use the array index
where necessary and store the server id within the array

To test:
1 - Add some new Z3950 servers, they don't need to be valid
    FIRST
    SECOND
    THIRD
    FOURTH
2 - Adjust the ranking so FOURTH:1 THIRD:2 SECOND:3 FIRST:4
3 - Enable and launch the advanced editor
4 - Click 'Advanced' under search on the left
5 - Note the list displays in the order you entered the servers
6 - Apply patch
7 - Reload
8 - Order is correct
9 - With valid servers, confirm that searching still works and servers can be checked or unchecked to include/remove from results

https://bugs.koha-community.org/show_bug.cgi?id=17515

Signed-off-by: B Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>