use display instead of send_figure in inline backend hooks This lets custom display functions (e.g. HTML) be used without any extra changes (see #2234). possible downsides: * The previous code guarantees that only one format is published. If multiple figure formatters are registered, display will send them all. * If people for some reason disable the type-printers, then they will display the automatic figure display. Neither of these cases can come up unless people are messing with the formatters, and I think the first is actually an improvement.