Bug 21911: Fix OPAC scoping to work with new group system

Bug 21911: Fix OPAC scoping to work with new group system

To test:

0 - Apply patch
1 - Create a library group enabled for opac search limits and add some
libraries
2 - Check the DB (or advanced search dropdown) to get the id of the
group (using 7 as example below)
3 - Add to apache configuration (OPAC virtualhost)
   SetEnv OPAC_SEARCH_LIMIT branch:multibranchlimit-7
   SetEnv OPAC_LIMIT_OVERRIDE 1
   RequestHeader add X-Koha-SetEnv "OPAC_SEARCH_LIMIT
   branch:multibranchlimit-7"
   RequestHeader add X-Koha-SetEnv "OPAC_LIMIT_OVERRIDE 1"
4 - Ensure OpacAddMastheadLibraryPulldown is disabled
5 - Restart all the things
6 - Visit the opac
7 - Perform a search, confirm it is scoped to the branches in the group

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>