Bug 20157: Use group 'features' to decide which groups to use for group searching...

Bug 20157: Use group 'features' to decide which groups to use for group searching functionality

Instead of basing the group searches on the group name, which is an
inherently touchy system, we should use the same checkbox style that
Jonathan introduced for the patron limits by group feature.

Test Plan:
1) Check to ensure existing group searches still show as they used to

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>