Do not exclude "identifier" facets by default

Do not exclude "identifier" facets by default

No longer ignore "identifier" fields when collecting and caching
facet data.  This change causes all config.metabib_field's that are
marked as facet_fields to be taken into consideration.

Apart from marking a field as facet_field=false, it's also possible to
control which fields are visible within the jspac and tpac (pending LP
911908)

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Mike Rylander <mrylander@gmail.com>