LP#1922273: use a setting to determine which advanced search filters are displayed...

LP#1922273: use a setting to determine which advanced search filters are displayed in staff catalog

The TPAC allows admins to customize which search filters are available
in advanced search.  This commit adds an org unit setting,
eg.staffcat.search_filters, which lets you customize search filters in
the staff catalog.  The setting value should be an array of filter
types, e.g. ["item_lang","audience","lit_form"].  The standard set of
search filters is used when the settings are not set.

Signed-off-by: Jeff Davis <jdavis@sitka.bclibraries.ca>
Signed-off-by: Terran McCanna <tmccanna@georgialibraries.org>
Signed-off-by: Galen Charlton <gmc@equinoxOLI.org>