Add callback to massage CFs on BulkCustomFields element

In some cases, we might want to remove custom fields from the list of
available custom fields for bulk update. This patch adds a callback to
the BulkCustomFields element to allow for this.

Author: richieri-bps

share/html/Elements/BulkCustomFields

@@ -143,4 +143,6 @@ $CustomFields
 </%ARGS>
 <%INIT>
 return unless $CustomFields->Count;
+
+$m->callback( %ARGS, CallbackName => 'MassageCustomFields', CustomFields => $CustomFields );
 </%INIT>