Bug 36545: Use select2 in item search

Bug 36545: Use select2 in item search

This patch modifies the multi-select fields in the item search to use
the select2 framework.

To test:
1. Apply patch
2. Go to staff interface -> "Item search"
3. Check item search form and search for
      - Home library
      - Current library
      - Shelving location
      - Item type
      - Collection
      - Status
      - Lost
      - Withdrawn
      - Damaged
4. Search with multiple variations (nothing selected, only one value,
   multiple values, ...) If no value is selected this means that "All"
   values are searched
5. Check that the search is working well

Sponsored-by: Karlsruhe Institute of Technology (KIT)
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
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>