Bug 15565: Add 'DisplayMultiItemHolds' system preference to toggle display of multi...

Bug 15565: Add 'DisplayMultiItemHolds' system preference to toggle display of multi item holds

These patches allow the display of checkboxes instead of radio buttons for placing specific
item holds in the OPAC and staff interface. This display is controlled by the system preference
'DisplayMultiItemHolds'. When disabled, the hold display is the same as in the past. When enabled,
the user can select multiple items to place holds on at the same time.

If there is an error placing one or more holds, an error will display on the following screen.

Test plan:
0. Apply the patches and koha-plack --reload kohadev
1. Enable 'DisplayMultiItemHolds' syspref
2. In staff interface, go to a record with multiple holdable items
3. Check the boxes next to 2+ items and click the button to place the holds
4. Note that the holds are all placed (unless there is a failure)
5. Cancel the holds, and try again (but this time make Holds per record (count) only
1 in the circ rules)
6. Note that one of the holds is placed, but the others are not and an error message
is displayed saying that one or more holds could not be placed because the holds per
record was exceeded

7. Perform the same above procedure on the OPAC
8. If DisplayMultiPlaceHold is enabled, you can test placing multiple specific item holds
across multiple bibs in the OPAC via the search results
9. If EnableItemGroups and EnableItemGroupHolds is enabled, you can test that you can
either place item group holds or specific item holds. Toggling the checkboxes in the
staff interface will uncheck the item group hold radio button.

Signed-off-by: Lisette Scheer <lisette@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>