Bug 24291: Update the item type form text for library limitation field

Bug 24291: Update the item type form text for library limitation field

Bug 15497 introduced the ability to limit item types by library.
However, the text next to the 'Library limitation' selection field on
the item type form mentions authorized values and is confusing.

The current text reads: "Select 'All libraries' if this authorized value
must be displayed all the time. Otherwise select libraries you want to
associate with this value."

This patch updates the text on the item type add or edit form for the
'Library limitation' field to something more understandable.

To test:
1) Apply the patch
2) Go to Administration > Basic parameters > Item types
3) Click 'Edit' for any item type
4) The text next to the 'Library limitation' field should now show
"Select 'All libraries' if all libraries use this item type. Otherwise,
select the specific libraries that use this item type."
5) Sign off

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>