Make it possible to trigger editor events with custom arguments

In some case, using custom editors, one might want to have editor events trigger with extra arguments. For now, the event editor handling is made by:

    // in form.js
    handleEditorEvent: function(event, editor) {
        var formEvent = editor.key+':'+event;
        this.trigger.call(this, formEvent, this, editor);
        ...
    }

And every argument passed by the event `event` on the editor are lost at this point. This PR tries to fix it.

Thanks !