Bug 6419: (follow-up) Use Select2 with optgroups

Bug 6419: (follow-up) Use Select2 with optgroups

This patch divides the OPAC and staff options into separate optgroups
and adds Select2 for styling and filtering.

THe patch also corrects a few missed instances of "Intranet" in the list
of location options on the entry form.

Signed-off-by: Caroline Cyr La Rose <caroline.cyr-la-rose@inlibro.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>