patron lookup is broken

Description: Clicking a filter or entering a search via the "Patron lookup" link shows a blank pane.

Details: Same as the find-user plugin for managing proxies, the table-header values instead of the keys are being passed through to the MCL. Before i18n was implemented, this was fine as values could be used for keys, but since the values will change when translated this is no longer the case and the keys must be used instead.