Bug 35329: Move patron search to modal - funds

Bug 35329: Move patron search to modal - funds

This is a tricky one.
We can have several modals per page, patron-search.inc needs to be
adjusted to not use ids but classes. Also we need to declare JS
variables with 'var' instead of 'let' (which does not allow redefinition
of the same variable).

Test plan:
Create or modify a fund
"Select owner" and "Add users" to open the modals.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>