Bug 36545: (follow-up) Style tweaks for Select2 multiple fields

Bug 36545: (follow-up) Style tweaks for Select2 multiple fields

This patch does some fine-tuning of Select2 style on fields which accept
multiple selections. The patch also changes the way the form rows are
displayed on this page. I thought that the Select2 fields should be
wider to accpet multiple selections without the container wrapping onto
another line.

The patch also sets the Select2 "closeOnSelect" option to false on this
page because I think that makes more sense in a situation where multiple
selections might be made.

To test, apply the patch and clear your browser cache.

- Go to item search in the staff client
- Confirm that the form looks good and adjusts well to various browser
  widths.
- Make some selections to confirm that the style of selections looks
  good and that the dropdown stays open as you make multiple selections.

Signed-off-by: Michaela Sieber <michaela.sieber@kit.edu>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>