Add a preference to specify what to show on the policy target column.

The new default is to only show categories.
Existing installations will have the preference set to both.
All the user defined protocols and categories are shown regardless of the preference (as not-editable fields in case).

scripts/lua/modules/prefs_menu.lua

@@ -247,6 +247,9 @@ local menu_subpages = {
     }, captive_portal_url = {
       title       = i18n("prefs.captive_portal_url_title"),
       description = i18n("prefs.captive_portal_url_description"),
+    }, policy_target_type = {
+      title       = i18n("prefs.policy_target_type"),
+      description = i18n("prefs.policy_target_type_description"),
     }
   }},
 }