2291249 Modal display

This is a way to allow display plugins to add an ajax event to the form.  I don't think this is the final way to impelment this, but I wanted to get something working so we can discuss.  It works for the modal, but for some reason it prevents the iFrame propogateSelection function from running.  It seems after the event listener is added it doesn't get called by the event dispatcher. It seems to be missing from the dispatcher at the time when the response event is called.