Bug 19524: Share patron lists between staff

Bug 19524: Share patron lists between staff

Some libraries would like to allow arbitrary lists to be used by all
librarians with the 'manage_patron_lists' permission.

Test Plan:
1) Apply this patch
2) Run updatedatabase.pl
3) Create or find two patrons with the manage_patron_lists permission
4) Using the first patron, create two new lists, mark one of them as
   shared
5) Log in as the second patron, browse to the patron lists page
6) Note the second patron can view, add and remove patrons from
   the shared list owned by the first patron

Signed-off-by: George Williams <george@nekls.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>