Improve UI of admin site settings (#4163)

app/models/form/admin_settings.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class Form::AdminSettings
+  include ActiveModel::Model
+
+  delegate(
+    :site_contact_username,
+    :site_contact_username=,
+    :site_contact_email,
+    :site_contact_email=,
+    :site_title,
+    :site_title=,
+    :site_description,
+    :site_description=,
+    :site_extended_description,
+    :site_extended_description=,
+    :site_terms,
+    :site_terms=,
+    :open_registrations,
+    :open_registrations=,
+    :closed_registrations_message,
+    :closed_registrations_message=,
+    :open_deletion,
+    :open_deletion=,
+    :timeline_preview,
+    :timeline_preview=,
+    to: Setting
+  )
+end