Bug 24254: Add Koha::Items->filter_by_visible_in_opac

Bug 24254: Add Koha::Items->filter_by_visible_in_opac

This patch adds a method based on the original idea from Nick, but on
Koha::Items.

The idea is to build a proper filter, based on the current rules for
hiding things, directly on the DBIC query. The caller takes care of
knowing if the filtering should apply (i.e. checking the patron category
exceptions) and then it would do something like:

    my @items;
    if ( <patron_category_does_not_have_exception> ) {
        @items = $biblio->items->filter_by_visible_in_opac(
            {
                rules => $rules
            }
        );
    }
    else {
        # still want to enforce 'hidelostitems'
        @items = $biblio->items->filter_by_visible_in_opac;
    }

To test:
1. Apply this patches
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Items.t
=> SUCCESS: Tests pass!
3. Look at the use cases on the tests, read the code
=> SUCCESS: It all makes sense
4. Compare with Koha::Item->hidden_in_opac
=> SUCCESS: It all makes sense
5. Sign off :-D

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>