Bug 28782: Use query param list instead of splitting elements using '/'

Bug 28782: Use query param list instead of splitting elements using '/'

This removes the need to handle single and multiple cases separately,
thus removing bunch if-else cases and simplifying our code. This
coding style is also in line with our other .pl scripts.

To test:
 1) Make sure placing a hold still works from the following pages:

   /cgi-bin/koha/catalogue/detail.pl?biblionumber=XXX

   /cgi-bin/koha/catalogue/search.pl?q=a

   /cgi-bin/koha/virtualshelves/shelves.pl?op=view&shelfnumber=XXXX

   /cgi-bin/koha/clubs/clubs.pl (create a new club and add a patron
   there and through the clubs.pl create a hold to a bib)

Signed-off-by: Hayley Pelham <hayleypelham@catalyst.net.nz>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>