Somewhere to actually turn the USB kiosk on

The kiosk page tells an administrator to enable it in Settings under USB. That
place did not exist - the setting was reachable only through the API or a shell,
which is the same trap the backups plugin shipped with. A settings page and a
catalogue card, so the instruction leads somewhere.

plugins/usb/frontend/routes.js

@@ -25,6 +25,12 @@ export default [
     name: 'usb-edit',
     component: () => import('./views/USBForm.vue'),
     meta: { requiresAuth: true, plugin: 'usb' }
+  },
+  {
+    path: 'settings/usb',
+    name: 'settings-usb',
+    component: () => import('./views/USBSettings.vue'),
+    meta: { requiresAuth: true, requiresAdmin: true, plugin: 'usb' }
   }
 ]