Bug 11256: Opac: Set a number of items to display on a biblio detail page.

Bug 11256: Opac: Set a number of items to display on a biblio detail page.

Currently, the number of items to display is hardcoded (50).
But the perl script loads all items before to check if the number of
items is oversized.

This patch adds a new pref OpacMaxItemsToDisplay (default to 50). If the
*total* number of items for a biblio is greater, no item is displayed
and a link allows to display all items.

Test plan:
1/ search a biblio with many items
2/ set the pref according the number of items you want to display
3/ verify the items are not displayed if the number of items is greater
the pref value
4/ enable the OpacSeparateHoldings pref and verify the items are
displayed in different tabs (if items have different locations).

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>