Fix maintainers form field
Fix maintainers form field

StationForm's maintainers was using improperly configured
django-ajax-selects.

aptiko/enhydris,kickapoo/enhydris,kickapoo/enhydris,aptiko/enhydris,openmeteo/enhydris,openmeteo/enhydris,ellak-monades-aristeias/enhydris,ellak-monades-aristeias/enhydris,ellak-monades-aristeias/enhydris,kickapoo/enhydris,aptiko/enhydris,openmeteo/enhydris