Added note when an object is unknown

refs https://github.com/TryGhost/Toolbox/issues/356

- this can occur when the ID in the action event is unknown in the DB,
  and we don't have any other context for it

ghost/admin/app/components/settings/audit-log/table.hbs

@@ -28,6 +28,8 @@
                             <LinkTo @route="editor.edit" @models={{array ev.resource.displayName ev.resource.id}} class="permalink">
                             <strong>{{if ev.resource.title ev.resource.title ev.resource.name}}</strong>
                             </LinkTo>
+                            {{else}}
+                            <small>(unknown)</small>
                             {{/if}}
                         </span>
                     </div>